Probably one of the simplest, most resourceful tools, is the hoko knife. In the Spring 2001 Society of Primitive Technology Bulletin, Dick Baugh published an article about an artifact recovered from a buried Indian site along the Hoko River in Washington state. Basically, it was a stone flake set into a small split stick and tied with bark cordage. (See: http://primitiveways.com/pt-hoko.html) This simple compression haft allowed you to use a sharp stone flake with greater handling and leverage. I have used it to cut strips of lacing from wet deer rawhide, using a fresh sharp flake, to sawing fireboard notches and felling small saplings with heavier serrated flakes.
Flintknapping, I have produced some aesthetically functional blades, but still some of the most resourceful and useful tools are the simplest.