Argthtjtr

Second Edit:

Thanks for all the upvotes. I just want to clarify one thing: I don't think I've done a good job in answering the OP's question. I think cr0's answer is much better for winter hiking. This little kit that I've put together is my 3-season emergency kit. Consider it the start of an emergency kit for the winter. [Also, since I have a fair amount of medical training, I usually carry a more comprehensive first aid kit (not pictured below), especially when hiking in groups.]

I've never done hut-to-hut winter hiking like the OP is describing. All of my winter hiking has been backpacking, where I've essentially got my shelter on my back whenever I'm not in it. This little kit I've got is what I use for day-hikes in spring, summer, and fall. If I were doing winter day-hiking in the environment the OP is asking about, I would add to my pack pretty much exactly what cr0 says.

Lastly, echoing cr0 again, having these items is not the same as knowing how to use them. You can get yourself into real problems even with these items.

Original post

Here's a pic of a small emergency kit I put together (plus the knife, compass, and whistle that were part of the 'normal' gear). Granted, this was for a summer (August) hike in the White Mountains of New Hampshire, USA. However, getting lost above treeline the weekend I was there could have easily killed someone from hypothermia. So, even though this is my typical emergency kit that I carry with me (and I could make work given my experiences), it might not suit your needs for winter hiking. If I were doing more winter day hiking, I think I would bulk up my kit.

*see below for more details of the trip and the thought behind this kit

Waterproof bag to hold it all

• Protects the kit, plus you could gather water in it. In theory, if
  you can hold water in a container, you can boil the water. But, I've
  included some water treatment pills in the little pill holder. Also,
  nice little non-weight-bearing carabiner.

Heat Reflective Poncho

• Better than nothing. Wet is way worse than cold.

Water / weather proof matches

• You can't really see from the pic, but these are the type that
  should burn even in stiff winds and / or if they've gotten wet. Even so, they are in a water-'proof' container

Tinder / Water (treatment)

• Wax-infused cotton tabs for the tinder. Iodine water treatment pills
  (which I sealed inside of bits of a plastic straw to water-'proof').

390 kcal 'Meal Replacement' Bar

• I had to punch a hole in the foil wrapper to let out some packaged
  air; I resealed with duct tape. Fits inside of the soap holder /
  first aid kit.

First Aid Kit

• 
  

  Contains:

  
  
  
  
  
  1. Another whistle
  
  
  2. Signal mirror
  
  
  3. Alcohol prep pads
  
  
  4. band-aids
  
  
  5. gauze pads
  
  
  6. duct tape
  
  
  
  

Paracord

• I think I did about 30 feet. It's never enough, but it might do.
  Worst case, it burns, too.

All together, it weighs 14 ounces (about 0.3-0.4 kg) and is about the size of 2/3 of a Pringles can. I keep saying water-'proof' because, in my experience water is so damn hard to keep out! Ain't nothing waterproof, I don't care what they say!

first edit

*Further details: This was a trip where I (a reasonably experienced and trained backpacker) took my friend and his teen-aged daughter to backpack up to shelters, drop gear, and day hike up to the summit. Each one of us had our own kit; the point of this kit was that this was the backup kit for us when we day-hiked from the shelters to the summit.

A general note about weather in the White Mountains, even in August: It was nasty! (50+ mph winds; rainy, misty, nasty weather; just above freezing at the Hermit Lake shelters where we stayed, which was below the tree line). In fact, the weather was so bad that a AT thru-hiker (super inshape dude) we shared the shelter with literally could not walk against the wind up on the ridge. After my group decided to abandon the ascent, he tried, failed, and met back up with us. So, even though it was one of the hottest months in a very hot year, it was very dangerous weather where I think I could have used this kit to save myself, but I am damn glad that I did not have to!

As usual, skills are the lightest and most effective thing one can carry. From how to bushcraft useful things from natural materials, to clever ways to satisfy needs like signaling or navigation, to keeping a healthy state of mind.

Nonetheless, some useful items greatly increase chance of success / reduce chance of suffering. The less skills, the more reliance shifts to items. Because items aren't always reliable, can weigh down a hike, and sometimes call for special skills anyway, much better to start with skills! Now onto the items, a kit I've carried in very remote, very cold woods through good and bad:

Think in terms of elements, and in terms of marginal benefit. For example, carrying an axe is nice if you need a lot of wood, but it's very heavy and could be improved or worked around with a knife, downed debris, or even a folding saw. Therefore an axe has little marginal benefit - carry a knife instead.

Summary of Gear (the TL;DR if you want to skip details)

When I lay all this gear out on a table it is not much. A zip-lock bag of fire stuff rolled up; my water bottle/cup in a belt-pouch or backpack; a trauma kit with water purification tablets in another belt-pouch or backpack; tarp-poncho in its own pouch plus a zip-lock with rope and some bush-shelter-odds-and-ends all stored in a backpack; basic navigation/signaling tools and a knife in my pockets/belt. I should weigh it but I'd guess it's all under 5lbs not counting liquid water and clothing.

Fire

Redundant, rugged, and lightweight. Starting a fire with numb feet and fingers is not fun and it is easy to lose clear thinking during this process. Carry a light water-tight container (e.g. used zip-lock bag) with items discussed in Given limited space and weight what should I carry to get a fire going with damp wood?

• Storm proof matches


• at least two lighters, better yet if one is designed to be 'storm proof'


• fire starters (e.g. eco-friendly ones made of wood wool and flammable wax)


• Flint and magnesium stick


• Fixed-blade knife, probably at least 3" blade, the sharper and closer to full-tang the better


• Extra knife. "Two is one and one is none" - and you do not want to need to improvise a cutting tool in the cold winter woods!


• Some sort of flashlight. I generally have a headlamp and a crank-light. I keep this with my fire-kit or somewhere else more handy, as usually it's something I grab when I'm settling down in place at least for a few minutes to adjust to approaching night.

This entire bag can weigh very little. Before I go out I double check there's plenty of matches, at least a lighter, more fire starters than I think I'll need for a few days out there, and a flint stick. Then I stuff it in the bottom of my pack - if I'm starting a fire I can empty my back and stay put for a bit.

Water

Best to go out hydrated, carry water in yourself. Also carry a liter to start a hike with. Some people like carrying a single 1L container, others multiple small pouches, I don't think that matters. What matters is that you have a container you can boil water, preferably without poisoning yourself.

I carry a nested hard plastic container + steel cup. I also carry ~6-12 water purification tablets in my first-aid kit - very light, rarely used, but you'll be glad you have them if you need them. Lately, I've added two 1L pouches (usually empty) with a Sawyer Mini water filter in my 'daypack' or whatever outfit I have with me in the woods. I left the filter and pouches out of this post at first as it's more for weekend trips than day hikes, but it's so light and useful, it's good to have in the kit and at least one occasion I've been happy to have it on a casual hike turned longer exploration/adventure.

Shelter

Your clothing is the key here, and layers are the key to that. You should be able to go from sauna to frozen outdoors with the clothes you carry on your back or tied to your pack or waist.

When I'd wander in very cold remote woods I'd wear: thermal pants and top, rugged pants, insulated overalls, 2 thin-ish warm tops, insulated wind-breaking jacket, scarf/shemagh, bandanas in my pockets/pack, balaclava, beanie, thin gloves with dexterity, thick wind-breaking water-resistant mittens, thick and/or 2 pairs of socks, insulated water-resistant boots.

This pile of clothing will make a big difference if you simply curl up in a ball under some natural shelter. If you are improperly dressed, your situation is much worse. But also don't let your clothing encumber you too much, and be careful not to sweat.

Lastly, for a day hike you don't want to carry a whole tent or whatever, but some basic components save you a lot of trouble if you are forced to overnight. I am a huge fan of carrying a lightweight tarp, better yet a poncho-tarp. That plus plenty of rope and duct-tape, and if you can bare it carrying >6 tent stakes and some carabiners can help too. With that pound or two of gear, and your tough knife from the fire-kit, you can construct pretty solid make-shift shelters in just 2-4 hours if you are below the treeline. A cheaper or additional option to tarp poncho is a heavy duty large garbage bag like those used in construction; wrap up part of your kit in it for water protection, and you can use that garbage bag as a tarp, bucket, bed-bag, poncho, and more.

Navigation and signaling

I used to keep it simple with a good compass (which includes signaling mirror) and topographic map. I'd also have an emergency whistle on me somewhere. Working in the woods I now carry a radio and/or GPS emergency beacon (an InReach device) but I didn't used to.

First-aid

Pick-up a light-weight trauma kit and keep that in an accessible part of your pack. Accessible so that you can access it quickly while panicking and injured, and in a simple place to describe so you can communicate its location to someone else in distress if needed. For intentionally longer trips, different/more first-aid is called for, but for day trips a trauma kit will do. Maybe a basic manual booklet too, some kits come with that. Better yet - really to the point of necessity - is familiarizing yourself with the kit and getting first-responder training to begin with.

Add some good cold-weather camping snacks to first-aid in case you get hungry out there, and remember to restock snacks before the next trip :)

I have spent significant time in the backcountry in the winter. Last year I did an early season through hike of the Continental Divide Trail, spending months living in the snow.

Below is a list of some items I'd recommend bringing if you're going on a casual hike in the winter. You should not bring all of these at once. Consider the conditions, your objective, your risk tolerance, and your experience when choosing which of these are appropriate.

• Waterproof & windproof outer layer


• 
  Warm mid layer: Ideally something like a fleece that works when wet. Down is okay if there's no chance of it getting wet.


• Moisture-wicking base layer


• 
  Long pants or tights: They don't need to be waterproof unless conditions are really bad.


• 
  Sunglasses: ⚠️ Snow blindness is no joke.


• 
  Long warm socks: I got frostbite on my ankles once because I was wearing ankle socks. You're probably smarter than me on that front.


• 
  Waterproof mittens: I wouldn't bother bringing any gloves that aren't waterproof into the backcountry.


• 
  Scarf, buff, or neck gaiter: If the wind picks up, you're going to want something to cover your face. It doesn't need to be too bulky.


• 
  Gaiters: Wet feet can escalate into a serious problem. If you expect to be walking through loose snow for more than 8 hours, gaiters are a very good idea.


• 
  ResQLink Personal Locator Beacon: Satellite phones are expensive. The next best thing is a PLB. Keep it in an outside zippered pocket of your backpack. Should you find yourself in a life or death situation, this can send out a distress signal via satellite and quickly summon help. (~$200, no monthly fee)


• 
  Microspikes: If there's any chance of encountering icy conditions, bring some microspikes. They're small and light. If you aren't on high angle slopes they're as good as crampons. ($60)


• 
  High calorie snacks: Pick something that isn't going to freeze into a solid mass (e.g. potato chips, crackers, bread)


• Foil blanket


• 
  Sleeping bag, ground pad, and bivy sack: Even if you don't plan on spending the night, these may be worth bringing in case you get stranded somewhere.


• 
  Headlamp: ⚠️ Always always always bring a headlamp.


• 
  Camp stove, tea, hot chocolate: The ability to heat water and/or melt snow may be the difference between a dangerous situation and a relatively pleasant situation. Stop for a hot beverage if morale is starts getting low. :)


• Map and compass


• 
  Offline maps on your smartphone ⚠️ (e.g. Gaia GPS (Fair disclaimer, I work at Gaia GPS))


• Extra socks

First: buddies. Solo activities are inherently riskier.

Not that's out of the way, what kit is practical?

Extra insulation and extra wind/waterproofing. This may be just one item, but it's more likely to be a foil blanket, extra mid layer, and survival bag. If you stop moving, you stop generating as much heat, so you need insulation. The extra mid layer, fleece or similar can be used simply for comfort, while the foil blanket is light and can be worn under the outer layer of clothing or over the top. This can be left with a casualty if you go to get help. The bright orange survival bag is also a signal that shows up well against snow or vegetation. If another hiker sees a survival bag, they're likely to go and check.

When kayaking in the winter I carry something slightly better than a survival bag but also bright orange - a small group shelter, which can also be wrapped round an individual. I have a foil blanket as well. I also keep a foil blanket in my compact first aid kit for distance cycling, when space and weight are at a premium (except in the height of summer).

When winter kayaking and often when winter walking, I carry a thermos of hot drink. It's not meant strictly for emergency use, but tends to be started after the toughest part of the day and finished at the end of the trip.

As well as slightly more snacks than I expect to want, there's something to eat in my emergency kit (a long life snack bar of some sort).

It's not unknown for me to grab my entire kayaking emergency bag for a day hike in winter. That adds a first aid kit, head torch (useful if delayed until after dark) and light stick (a casualty is much easier to return to after dark if they've got a light source, and it's very comforting). There's other stuff in there that's less useful for hiking, but it doesn't weigh much and I prefer to keep the kit intact.

The ability to get exact coordinates and send them to someone useful is important. SMS can still often get through with a patchy signal, as it should wait until it can connect, but recently we had more luck with a messaging app that sent as soon as it got a data signal (not an emergency, but good practice for one - two members of one of our two kayaking groups didn't do as much river as their boats did, but communication reunited then with most of their kit without excessive hanging around on river banks).

There are some good answers here from some people with solid experience in mountains in the winter. However, these answers seem to slant extremely heavy on gear. Sometimes it's reasonable to do a day hike in winter in the mountains in a lightweight style, but you do want to be carrying the crucial things in your lightweight kit.

The first thing to do is to try to get a weather forecast that is as up to date as possible. If there is the possibility of rain rather than snow, then you want to have a plan for how to deal with getting wet, or to avoid getting wet. If the conditions are forecast to be very bad (extremely cold, extemely windy), then just don't go; don't get locked into a mentality where you have to go because it's your day off from work, or whatever.

I'll assume that the situation being envisioned here is one in which only snow, not rain, is likely. Then there is basically a very simple and lightweight set of gear that you need, to avoid the situation described in the question:

1. A PLB. It's simple and lightweight, and if you're really stuck, it's a life-line.




2. A GPS unit that is not a phone, i.e., that doesn't depend on access to the cell phone network.




3. A map with an appropriate coordinate system marked in.




4. A compass.

So for the person who died in the incident you described, basically the life-saving steps that probably would have worked would have been to consult the GPS, find coordinates, locate himself on the map, figure out the heading to get to the nearby mountain hut, and then use that compass to move along that heading.

In the event that he can't do the above, e.g., because of injury, an emergency backup is to activate the PLB.

The safest concept is to always plan for the worst case. Of course, best practice varies according to context. Whether you're going solo or in a group, the equipment will change. Same goes for the different seasons. But generally, plan for slightly more than what you expect; i.e. if you're going on a day-trip, carry at least enough to overnight outside.

In your particular case, a solo hiker in the winter, it becomes somewhat of a tradeoff. In a group, for a day-trip, there should always be someone carrying a sleeping bag in case someone gets injured and immobilized. That is alongside an emergency kit. It adds up quickly in bulk and weight, but when you can divide it among a group, it's easier to manage.

Carrying a sleeping bag becomes slightly cumbersome for one person on a day-hike, so it's usually replaced by an insulated parka. If you can keep your core warm, you can last a while. Anyway, the parka usually gets used if taking longer breaks, provided the hiker doesn't overdress to begin with.

As for an emergency kit, it doesn't need to be that large. A means to start a fire and a good quality space-blanket already cover the most essential pieces of equipment to overnight in cold weather. Those take up almost no space in a pack and there is no reason not to carry them.

I personally do solo-hike in -25°C weather regularly and my 32 liter pack is pre-made, hung in the gear-room. It's a bit overkill as I carry a way too large first-aid kit although it's more in case I need to help others. Strapped on the side is a thin 5mm EVA sleeping pad which is part of the E-kit. Then the rest is clothing, which usually consists of upper and lower waterproof outer layers, a down parka, two pairs of insulated gloves (in case one gets waterlogged), multiple pairs of polypropylene liner gloves, a pair of spare liner socks, plus 2L of water, some dry snacks (nuts, fruit bars, cheese), etc. I know I could overnight with that gear. It wouldn't be comfortable, but enough to stay warm. Bear in mind, this is all gear that I carry but almost never wear. It weighs about 8kg, which is not too much, and I consider it training weight so I keep the muscle memory.

The most important part of the puzzle though is not necessarily what I carry but what I know about using it. Any serious outdoorsman/woman should consider taking wilderness safety/first-aid courses and practice/revise their knowledge regularly.

Given that the OP said Europe, the advice should always include seeking local advice because there are a wide variety of conditions in Europe driven by the effects of the Gulf stream that can be significantly different to the conditions in North America. There are areas that have similar continental weather, but the mild oceanic aspects in winter can really make a difference (especially in UK/Ireland).

It is also important to decide if the kit is about overnight survival, or about about incident response. They have different imperatives.

A survival bag is very worth while for both overnight and casualty incident response. Is should be sturdy enough to protect from wind and rain (or sleet/wet snow). You should try it out, just getting the whole body out of the wind will make you feel warm, just like stepping inside a cabin/hut.

Some spare clothing (or maybe light weight sleeping bag for benightings) is also good, along with gloves/hat/scarf. A bit of emergency rations should also be taken - I take marzipan (you can't eat it all at once - try it!). A torch is very useful for overnights and signalling.

Then it's back to getting local advice, and while you are at it, tell them/someone where you are going and expect to be back.

This query started with a local accident. Yeah. We get so many of these. I was moved by the James Kim story. For the want of a nail...

Have a 406MHz ELT

Every big player from the Royal Navy to Emirates wants a world-class global locator beacon system that works anywhere. However, the infrastructure cost of a worldwide system is simply too high to sustain two systems. And one system would necessarily have a lot of spare capacity. So lucky us, we get to use the same system as the Air Force. The 406 MHz system has protocols for the ELT to acquire your GPS coordinates and transmit them direct to satellites, along with your unit's serial number.

406 is officially called CoSPAS-SARSat, and is a joint US-Soviet (really) system, which has been upgraded to support GPS. Several other nations came on board, and all their SAR satellites are networked. This system is run by governments.

They (the responsible government SAR branch*) will know who you are before they rescue you, if you register the unit. They will have already tried your phone.

Cost of a unit is $250-ish, and there are no costs after that. Even the rescue is free in most cases. It's bad public policy to charge people for rescue, because fear of the costs could get them killed.

Nomenclature note: When an "Emergency Locator Transmitter" is packaged into a handheld unit, it's called "Personal Locator Beacon".

A flaw in the 406 system is the inability to send non-emergency messages, this drives people into technically inferior systems like SPoT.

The more serious problem is they are not reliable in extremely adverse geography like a slot canyon. The unit has to be able to see a chunk of the sky. But nothing else will get a signal either.

Backup system? You could try failing over onto an Iridium phone or SpOT, but that system is largely inferior. I would consider a second 406. An old 121 MHz beacon is helpful once the air patrol is in line of sight or if a passing jetliner happens to be monitoring 121 MHz, as they sometimes do. But 406 PLBs include that, so a spare 121 would come into play after a 406’s battery ran down.

Bring what you need to hunker down and await rescue

Beyond that, your emergency supplies should be all about keeping you alive until the weather is good enough for SAR to operate and reach you. You should have everything you need to survive the next night or two, or longer, depending on the weather forecast.

Since that is so dependent on local conditions, I can't advise.

* by "local SAR branch" I mean the worldwide system looks at the location, delegating to the country who then delegates to the competent local authority, so it could be CalFire, CHP if you're in a freeway junction, airport rescue if the location is inside the fence, Russian Coast Guard, etc.

To start with, there is no such "list" which can adequately cover your question- every trip is different, every scenario is variable, and winter is such a broad period that regions have completely different challenges ("winter" in the Northern Hemisphere happens in a different part of the calendar year than it does in the Southern Hemisphere, and January in the Front Range of the Colorado Rockies varies drastically from March in the same location varies drastically from the Western Slope 100 miles West). Additionally, hypothermia can easily be suffered in July or August (at 2000m elevation, in July temps can be under 10C at night, even start dropping in the 10-15C range by dusk).

The only constant item you will always bring with you is your brain; that may sound flippant or impudent, but I mean it quite sincerely. Going into the wilderness without proper knowledge and education is the first potentially life-threatening mistake you can make (you referenced not knowing how to erect improvised shelter). Next, if you lose your head and start to panic, you will be in a world of hurt; education is the foundation here.

Have you taken a Wilderness First Aid course? Are you aware that, if you require assistance by a Search and Rescue team, it can take over an hour just to transport you 0.75km (0.5mi)- not counting the time it takes to call them, SAR to organize and respond, response time, travel time to you, patient evaluation, patient package for transport, handoff to EMS personnel, transport to hospital? Do you know how to handle an injury in the backcountry and the exponentially complex nature of something as simple as a blister which wasn't managed properly when you are in the backcountry versus front country (e.g. your house)? Do you have a proper first aid kit and know how to use it?

Next is basic survival skills. This doesn't have to be an expensive class by any means. There are usually groups which will teach basic skills in wilderness survival and how to keep warm and dry.

As for gear, backcountry medicine and survival is 90% improvisation, so a good class will teach you goal oriented skills and how to improvise with the items you always carry. ab2 referenced trekking poles and I agree; I always walk with them (when I was a guide one of the guys on my team used to call them "wussy wands" and I love the term- especially since he now uses them). They will reduce strain on your back, knees and ankles and they are incredibly versatile- splints for instability in limbs/joints, improvised shelter building, etc. a base list might include (but is not limited to):

• Aforementioned trekking poles
  emergency blanket (the heavy duty kind such as those made by SOL, not the cheap limar "space" blankets)


• Cravat (x4)


• SAM splint


• Fire starter (flint and steel and nesting material- practice and know how to use them)


• Signalling materials (I like the Silva Ranger compass with mirror and sighting slot, Storm(tm) whistle, and the flint and my fire building material is also for signalling)


• Navigation tools (manual, NOT your phone or GPS, and know how to use it- the compass serves double duty here, and carry a map of the region in which you a traveling)


• First Aid kit; a real one- no off the shelf first aid kit I've found is sufficient or effective. They're usually "150 parts" 145 of which are useless in the backcountry, or made for x number of people for y number of days and are way overpriced and full of a bunch of junk you won't use, missing stuff you need, and have a little first aid book which won't do you much good in an emergency ("let me see, you're bleeding out...bleeding..bleeding...ah! 'uncontrolled bleeding, what to do' page 18, 72, 101...okay..give me a minute to look that up..."). Take a WFA or WFR course, know how to use it and what to do.

This may sound like a lot and very expensive (and some may say overkill for a day hike), but the listed items actually aren't that substantial in size/weight and a day hike is something which seems like a simple activity which doesn't require more than shoes and a water bottle, but it can quickly become life threatening.

Permit me to relate an anecdote here:

A couple of students of mine were enjoying a day hike on a trail just outside Boulder, Colorado (about 30 minutes from the hospital) when, about 1.5mi (~2.4km) in they encountered a young lady on her way to the trailhead to call for help (they were in a canyon and reception was spotty). She said her friend had "fallen" and was hurt so, having recently completed their Wilderness First Aid course, had their first aid kits with them and went to check on her.

The patient had fallen 20ft (6m) from a rock and was in pretty bad shape. The two young ladies requiring assistance were on a simple day hike in July in a well known area close to town, and were taking a short break on an overlook to take in the view when the patient slipped and fell. it took 13 hours to get her to the hospital. They had no first aid training, no first aid materials (just hiking shoes, snacks and water) and no survival materials (shorts and t-shirts for summer weather). Worst of all, no training of any kind and so no ability to improvise with what they did have.

Luckily, the friend did have her cell phone, kept her wits about her, and knew enough to make sure her friend was breathing and went for help. They just got lucky in that some trained and well prepared people were on the trail ready to render assistance.

EDIT IN RESPONSE TO COMMENTS:

My apologies for not making the connection on the use of my anecdote clear- the point of the anecdote is to drive home the importance of training and the difference it makes to have someone with training versus being without, and illustrate how complicated it can be even with training. The reason for that one in particular- even though a summer example- is that the question was directly related to a day hike close to the front-country and people often minimize the necessity of being prepared with a solid first aid kit, but that it is a potentially fatal mistake to make.

As for cravats, their inclusion in my list is not a typo- in my opinion, they are the most underrated yet versatile item you can carry in your pack- build a shelter, stop bleeding, make a splint, improvise and you can come up with hundreds of uses. The reason for four is that, with four, I can effectively splint and package any limb fully and completely. Can I do it with less- sure, I don't actually need any, but they take up so little weight and space that, at $0.89, why wouldn't I carry four?

Regarding off the shelf first-aid kits, I have yet to find one which I wasn't, in the end, having to replace so much of the contents that I ended up using it for just the bag. They are made to make money- the contents, while great at home, are neither the quality nor are they of the type that I need in a good kit. I don't need a set amount of items, I need to change my kit depending upon which activity and duration I am doing. I need to change a dressing on a wound every 24 hours in the backcountry. Assuming I need to be prepared to handle wounds which may require a 3x3 gauze pad and a roller gauze to dress (not counting irrigation and infection mitigation), if I'm on a twelve day trip in the desert and I get a 4" laceration on my shin falling while setting up a rock climbing route on day two (happened to me), how much gauze do I need to be prepared with to manage that wound and prevent infection? Chances are, I won't have to dress it the entire time (in fact, I shouldn't if I don't have to) and bandaging, so long as it's clean, may be reused so I may not need to account for every day but, if I see signs of infection, I need to change it more often and keep it covered longer.

In this case, I was also one of the trip guides, so I'm carrying a larger kit due to the fact that I'm prepared not only to take care of at least 3 wounds for myself, but at least 3 from trip members (they are carrying their own too, but I need to be able to have materials ready at hand). Even so, For just this one wound, I have a pair of nitrile gloves, 3x3 gauze, roller gauze, povidone iodine wipe, and alcohol wipe for each for 11 days x1.5 (for infection) when I leave. A lot? sounds like it, but I'm not interested in cancelling a trip because I wasn't able to manage a simple wound. I also have that x5 (I've got enough for several wounds remember), plus material for a major bleed event, splinting material, sting/allergen material, signalling and TIH mitigation, etc. Sounds like my FA kit is as large as my trauma kit on the Engine in my station, but it isn't, it's broken into a few small kits, 3x3x4/5/6, placed in the voids in the top of my pack. For shorter trips or day hikes, it gets smaller based upon duration of trip and activity, all fits in a single small bag. No off the shelf has more than a couple of gloves, a couple gauze pads, maybe 1 or 2 roller guaze.

I can't get into wound cleaning and management here. I'm not teaching a wound class, so I won't get into the data on the benefits of wounds being left open and moist versus covered and dry, closure vs non, how to use povidone iodine and alcohol, when absolutely NOT to, what to use for irrigation and how, etc. I can't cover how to properly recognize wound infection, the seriousness of it in the backcountry (4, 8, 10, 18 hrs are the times to watch for it initially), highest risk areas of the body, etc. There is a lot there (few hours of class), not will I try- that's a hands-on class, and takes a lot of time. Thus, take a class in backcountry medicine and learn what you need to know to mitigate these things, how to manage them, and what it takes to actually treat and manage a wound, and you quickly begin to see off the shelf first aid kits in a whole new light (at least, I do- they are heavier and bulkier than mine, and lack the equipment I need to manage even a single wound in the backcountry).

It has been my experience that, the longer our trips get, the lighter we try to make our packs but the heavier our first aid kits, by necessity, will get. Can an argument be made that it's all overkill, totally unnecessary and you can get by with much less? Sure. It's called confirmation bias. Everyone has their own opinion on these things, and I'm not claiming to be an expert, I'm answering from my own experience from 30 years of recreational, guide, military, and rescue experience.

I'd add a space blanket to each person - one of those thin mylar foil things worth a couple dollars. They're not heavy, and while they're not perfect its better than being caught in the cold with nothing warm.

They're not a coat but they are waterproof, so will stop you getting more wet in the rain.

https://en.wikipedia.org/wiki/Space_blanket

Why one per person? Because its no use having all your stuff in the bag of the strongest person, when someone else gets lost.

Lots of good and valid points in the existing answers, but I'd like to add a few points from a Central European perspective, and for situations that are as described i.e. the serviced lodges are not seen as a nice find in a tour that was set up as winter camping. For alpine tours I'd probably take some more gear (see lists from the other answers).

• Main message: someone who is up and walking (i.e. not drunk/drugged, not unconscious or otherwise immobile after an accident, and not soaked after falling into a river/lake etc., and did not loose the clothing that was basically adequate for the tour) usually does not get hypothermia unless they are exhausted/hungry and tired. (often accompanied also by being dehydrated)
  
  So, avoid exhaustion.
  
  And IMHO the most important thing to carry (that is different from summer gear) is: bring more food and make sure you eat and drink regularly. Enough = sufficient to keep you well fed through the night in case you don't reach the hut for whatever reason.
  
  BTW: I've found diluted juice (possibly with hot water at the start) a very good ration for the first part of a tour. Or putting sugar into the hut tea. Also, very cold weather can be deceptive in that you may not realize how much water you actually loose (by breathing) - but this is rarely reached in a temperate climate (I wouldn't call an alpine mountain climate temperate).




• Realize how much reserves/safety margin are needed. E.g. having a working knowledge of how mich strength it costs to hike a distance that would be an easy stroll in good conditions if there's half a meter of snow with a crust that doesn't carry you but instead has you break in at every single step. Or a driving rain at +2°C against you for hours and hours.
  
  Know when to turn. Turn half an hour before.




• Winter tours, particularly if solo, should be decidedly on the easy side to leave sufficient safety margin for bad conditions and/or accidents (even if you just find someone who had an accident) or the odd loop of 3 hours in the fog.
  
  Misjudgment that makes a tour miserable in summer can be decidedly dangerous in winter.




• There are some vicious cycles that you should know and recognize (a buddy can help with that). One very typical in winter day tour is IMHO "I don't want to take a break - I'll be getting cold". This is IMHO a sign that a break is overdue. In my experience at this point both eating and drinking have usually been neglected for quite a while. Knowing that stopping would make you cold means that you're already slightly exhausted. Unless you're used to being outdoors all day it is easy to underestimate how strenuous this can be in winter weather. Exhaustion means that both the risk of accidents increases a lot (plus you're much less able to cope with that accident) and hypothermia lurks around the corner even without accident.




• Similar to the vicious cycle above is realizing that, say, your fingers/hands are cold - and being reluctant to warm them up, say, under your armpits, because even opening your jacket a bit (possibly stopping and turning your back against the wind) will make you cold. Or realizing your feet are cold, but you are too tired = exhausted to start jumping around.




• In addition to the raingear which is in the kit all year round, bring a set of thermo underwear (shirt + long johns weight basically nothing and improve insulation a lot, putting it on even in shitty weather will pay off soon in terms of warmth), additional wooly cap + mittens. Make sure your layers are large enough to go over each other.
  
  In addition, the stuff I bring for "intended" use includes at least one additional layer that will keep me comfortable during longer breaks and outdoors after the strenuous tour is over (again like in summer). But then, people tell me I carry crazy amounts of stuff - but are somewhat more often than just occasionally quite happy if I lend a fleece or gloves or ...

• Compared to the answers that are more on the wilderness side, I bring much less first aid stuff in Central European "day-tour regions" - all you need here is typically to keep someone who had an accident from getting much worse until help comes - which may be more than an hour, but in most regions you don't need to plan for surviving days until found. The one thing that differs for the winter vs. summer day tour kit is again insulation and possibly food/drink.


• Mobile phone coverage, btw. is something that can be checked beforehand online. If the mobile phone is to be the rescue device, I keep it in an inner pocket and don't use it for normal navigation to keep the battery fresh and warm. Having the mobile phone's GPS find the location at the start of the tour is a good idea though - it will then take much less time to update the position if needed.