Ken, In a wilderness situation a knife would be fabricated from the same materials people used before metallurgy; lithic, bone,shell and even bamboo. It takes a little more skill than just haphasardly bashing two rocks together to flake a lithic blade. A large bone smashed with a cobble however will produce very keen edges. A librarian of classic antiquity was slashed to death by a mob wielding shells. Fabricating these items can be learned via the various "primitive movement" advocates. See Doug's link to Wilderness Way magazine. Some archaeological texts will demonstrate knapping.