Change and sip first. When you hit camp, swap wet layers for dry to limit heat loss. Then brew a hot, sweet drink to refuel, rehydrate, and reheat.
Limit breezes. Dig or stomp a tent platform six inches deep, so the edge of your rainfly is below the snow’s surface. Then cinch the fly as low as it will go.
Wear your bag to dinner. You’re suddenly sedentary, and temps are falling: Bring your sleeping pad and bag to the kitchen area, or retreat to the tent while your rice is cooking.
Cook before you camp. In extreme cold, break up your sedentary evening hours by stopping for dinner an hour from camp. Cook and eat, then warm up again as you finish the miles to camp.
Bring an extra pad. Double up on ground insulation: Put a closed-cell foam mat under a full-length, inflatable pad.
Go to bed warm. Do sit-ups inside your bag to generate body heat. Wear a hat and make sure your bag is sealed.
Add insulation. 1. Spread extra layers over you in the bag instead of wearing them, says Fierer. That way, you won’t crush their insulating power. 2. Drape a puffy jacket or vest around your shoulders, like a giant neck gaiter. 3. Wrap a shell around the foot of your bag for extra warmth and condensation protection. 4. Really cold? Cover the bag’s hood opening with a puffy jacket.
Have a midnight snack. Wake up cold? Eat a candy bar (store it in your bag).
Prevent condensation. Open fly vents or crack the door to allow a cross breeze. Pack a camp towel to wipe any frost and water droplets and frost that do form on the tent ceiling.