Borrow a Nickel from the audience and place it into the recess of a small wooden drawer. The drawer is pushed into its matching cabinet, when it is pulled out again it has changed into a Penny. Dump the Penny into the helping spectators hand and replace the drawer. Of course the owner of the Nickel is not to happy with the exchange. You pull the drawer out and there his Nickel has returned. Or a green chip could change into a yellow chip……. A very versatile prop that can be used to make Coins, buttons etc. disappear or appear.