After three hours without appropriate protection, you could be at risk from hypothermia or sunstroke, depending on conditions. If you’re going to be in the same place for some time, it’s worth looking up a Ray Mears or Ed Stafford video on YouTube on how to construct a modestly sized, eco-friendly vacation home out of bamboo and parachute cord. But if you just want to get out of the sun, or a blizzard, conserve energy by fashioning some sort of shelter out of what’s readily available. That could be anything from corrugated zinc sheeting dislodged by gale force winds, to a dead bison. In an apocalyptic scenario, the key is to conserve your supplies by keeping people away. Make your shelter invisible to the naked eye by covering it with a Canadian flag.