My kids have their own little art corner where they work on their paintings and such. They always do a rough sketch in pencil, draw over it and then erase. Almost inevitably I hear someone screaming at another someone over where they left the erasers. Then we spend the next half an hour looking for one. I recently came up with a simple solution:
A Hair band or two around the pencil cup does the trick. Any elastic will do. One band will hold several erasers or whatever small object you want on hand.