On the Trail
You’ll need more calories in cold weather. Pack food that won’t freeze, break it into easy-to-eat pieces, and store snacks close to your body. Good bets: chocolate, cookies, fatty nuts, and small chunks of cheese and salami.
Prevent your water from freezing.
Wrap bottles in wool socks or insulated carriers. Bring a wide-mouthed bottle; the larger surface area is less likely to freeze. Flip bottles upside down to prevent freezing at the top.
Pack cold-resistant lithium batteries (alkalines lose power in subfreezing temps).
Keep feet warm.
Wear oven bags (Werner likes Reynolds brand) under your socks; the nonbreathable layer prevents sweat from making socks and boots damp (more info on using vapor barriers in clothing).
Avoid low-lying campsites.
Cold air collects in valley bottoms.
Sleep with your boots.
Slip them into a stuffsack and store in your sleeping bag to avoid frozen footwear in the morning.
Boost internal warmth.
Place heat packs or hot water bottles where large arteries are pumping blood (like the femoral artery by your crotch).
Use a liquid-fuel stove.
They work in extreme cold, while most canister stoves don’t. Tip: Wrap the fuel bottle with duct tape to prevent cold injuries. Fuel makes the metal bottle freezing to the touch.