In his excellent book Bushcraft 101: A Field Guide to the Art of Wilderness Survival, survival expert Dave Canterbury goes through the “five Cs of survivability”: cutting tools, cover elements, combustion devices, containers, and cordages.

“Within these five base elements are all the tools and knowledge you need to be prepared for emergencies as well as to become independent of the trappings of the urban jungle,” Canterbury writes. “These items are the hardest to reproduce from natural material, take the largest amount of skill to reproduce, and control the conditions that most directly affect your body’s core temperature.”