Get some pieces of flint. When chipped together, they produce a clinking sound. Keep trying different sizes of flint until you find a sound that you like. Note that your instrument may be short-lived because the flint will flake away the more you strike it.
Hollow out a gourd -- a pumpkin or a squash will do -- and let it dry. Add dried seeds or small pebbles. Stitch the opening closed -- if you are a purist, use sinew -- and you have a basic rattle.
Hollow out a log for a drum frame, using a hammer and chisel. Keep working until about an inch of wood is left. Soak a leather hide or an animal skin over the log and tightly secure it with sinew, a drum ring or cord. As the skin dries, it shrinks and gets tighter, thus producing the hollow sound.
Clean out a sheep's horn and drill a hole in the end. Practice pursing your mouth in different positions and see how many sounds you can create with this prehistoric horn.
Make a bull-roarer. Drill a hole in a piece of bone, thread a leather thong through it and tie a knot in the end. Wave the bull-roarer over your head as fast as you can and dance to the whirling sound it produces.
Cut various lengths of wood and attach them on a frame with rawhide. Use the drumsticks, and you have an early version of a glockenspiel.