Warmth - Shelter - Water - Food
Once you have a fire going, turn your attention to preparing a shelter. Shelter will provide protection from the wind, snow, or rain and, properly planned, will trap heat from your fire.
Location - Instinctively, a low sheltered area may have appeal. Don't! Choose a site on high ground where you are visible, wind can clear insects and you will avoid the dampness held in low areas. In winter, of course, you should find the most protected (but convenient) location available.
Fallen Tree Shelter - The easiest from of shelter to find will likely be a fallen tree with ample space between the trunk and the ground. Often all you need to do to clear a shelter under the tree is to remove a few branches and lean them against the trunk to act as a crude form of roof. Boughs from nearby trees may also be added. Be careful not to remove any branches that may be supporting the tree above the ground. A bed of boughs at least 8 in (20 cm) thick will insulate you from the cold, damp ground.
Lean-to Shelter - A lean-to is simple to build. Locate two trees that are 6-8 feet (2-2.5m) apart. Fasten a sturdy pole to the two trees by using some cord from your pack, or hang the pole from the junctions where branches meet the tree trunk. The support pole should be 5-6 ft (1.7-2m) above the ground. Next, lean light poles about 10ft (3m) in length against the support pole. Space them about 18 in (0.5m) apart. Make the slope steep enough to shed water, but leave enough room inside. This rough frame can then be thatched with spruce or pine boughs, long grass, reeds or a sheet of plastic. Always start at the bottom and work up. Spruce boughs placed with the butt ends pointing up will shed the rain like a shingled roof. Be sure to close off the ends of your shelter. Make a bed of spruce or pine boughs or grass. Along with your fire, you can be quite comfortable. For maximum warmth, build your fire across the entire open side of the shelter.
Snow Shelters - Snow is an excellent insulator and in extreme weather conditions may provide the best type of shelter available. The major disadvantage in building snow shelters is the problem of getting wet, especially if you're not dressed for digging in the snow. Also, your task is made much easier if you have something to dig with, preferably a shovel, a snowshoe covered with a trash bag or something similar. Some practical experience in building snow shelters beforehand is also valuable.
Snow Cave - You can burrow into a large snow bank along a stream bank, rock outcrop or other place where the snow is deep enough. The finished snow shelter should be large enough to sit up in, so you may have to pile snow to achieve a mound big enough to tunnel into. Try to keep as dry as possible.
When shaping a snow cave, arch the roof inside so moisture from melting snow or condensation will run down the sides of the cave instead of dripping on you. The shelter should be shallow enough and the roof thin enough for you to break through and stand up if a cave-in occurs. You can block the entrance at night with a snow block or anything handy but leave a small ventilation hole. Besides the vent hole in the entrance way, a vent must also be poked through the roof. Keep the vent holes open by poking a stick through them occasionally.
Chop a roomy shelf, or build one, to act as a sleeping platform. Cover it with whatever material you can find; boughs, grass, reeds, etc. This shelf will keep you up off the cold floor. The closer you are to the ceiling, the warmer you will be.
Quin-zhee - The quin-zhee is similar to the snow cave with two important differences: you build the snow bank yourself, and a quin-zhee is stronger if properly built. Pile snow into a mound about 5 ft (1.5m) high and about 7-8 ft (2-2.5m) wide at the base. If you don't have anything that can act as a scoop, use your mitten-covered hands. Make sure the snow has been well mixed from top to ground; this is the key to building a strong quin-zhee.
Allow the pile to harden for fifteen minutes or so. The colder the weather, the faster it will harden. After it has hardened, tunnel into the base on the leeward side. Make every attempt to stay dry. Hollow out the mound, keeping the walls about 10 in (25 cm) thick at the base and at least 6 in (15 cm) thick at the ceiling. Poke a small stick through the walls occasionally to measure the thickness.
Keep the entrance as small as possible. Block it when you're inside with the snow block but leave a small air vent. Also poke a small vent in the ceiling. Build a sleeping bench up off the floor and cover it with boughs, reeds or anything else handy to insulate you from below. Candles will provide light and some warmth.
Staying dry - If your clothes are wet, you'd better try to dry them. Wet clothing will result in a loss of heat and energy that you cannot afford to lose, especially in cold weather.
Clothes may be dried by the fire, but never place them nearer to the fire than you can comfortably hold your hand. Never leave clothes unattended when they are drying near the fire. Turn them occasionally. Dry your outer clothing first, then take your underwear off, put on your outer clothing and dry your underwear. Put your underwear back on when it is dry.
It is most important to keep your feet and hands dry. Dry socks, mitts, and boots by suspending them carefully over the fire. If socks and mitts are not too wet, they can be dried by placing them under your clothing overnight.
To avoid becoming damp through perspiration, dress lightly while you are working hard and put on heavier clothing when you are sitting around idle. If you are working with a parka on, leave the hood down and leave it open around the neck to allow excess heat and moisture to escape. In very cold weather, damp clothes can be left to freeze and the moisture beaten out of them when still frozen.
Survival Guide - Warmth - Shelter - Water and Food