No matter how prepared you are for a survival scenario or anything for that matter something will happen. Gear breaks, gets lost, stolen, and forgotten. If you find yourself in the middle of nowhere in need of a cup or bowl this could help.
Piece of wood the rough size you need
a straw or reed
To start you need a nice hot bed of coals. Carve a small notch into the end of the wood and place a coal on it. Begin blowing on the coal and it will burn into the wood continue blowing on the coal with the straw until it has hollowed out the wood sufficiently for use. This is much faster, safer, and easier way to hollow wood than with a knife.