said by Hook_Texas:Depending on the size of the hole, golf tees work well too.
I've used *real*, wood golf tees for this type of repair. Just have to make sure they're not the 'soft' variety or ones made of a composite material.
As others have mentioned, and I've used myself, toothpicks really do work. There's no need to jam pack them into the hole so that no hole remains either. You just want to make the existing hole smaller.