The lean-to is the fastest shelter that actually protects you from wind and precipitation, and it's buildable solo with no tools.
- Find a ridge pole — a long, sturdy branch — and prop one end against a tree fork or two crossed sticks about waist-to-shoulder height. The other end rests on the ground.
- Lean shorter branches against both sides of the ridge pole at an angle, closest spacing on the side facing the wind.
- Layer debris — leaves, bark, pine boughs — over the frame, thickest where you need the most insulation. Aim for at least 4-6 inches of coverage; thin debris shelters fail at exactly the moment you need them.
- Build it smaller than feels necessary. A shelter sized tight to your body traps your body heat; an oversized one just traps cold air around you.
- Insulate the ground under you before you insulate the roof — you lose more heat to conduction against the ground than to convection from the air.
Priority order when time is short: ground insulation > wind block > roof. Hypothermia kills faster than getting wet.