if you don't know, watch "Naked and AFraid" on tV or youtube. The producers don't DARE drop off couples anyplace that is cold, cause they'd be dead in 3 days and all messed up (for TV viewing) in 24 hours. Perhaps in just an hour, depending upon wind, rain, available shelter. But guys walk around for hours at -40 F, if they are dressed for it. if you've got a decent setup of clothes on your person, another 2 lbs of cold weather clothing, and 3 lbs of the right shelter-sleep gear, you're good down to 10F degrees. The army says that nearly all enemy activity stops at such temps, so you are almost completely safe to build an intelligent sort of fire, heat rocks and water with it and use those to radiate heat, reducing how much fuel you need and by the same token, reduce how much time and effort you have to spend gathering fuel for that fire.
