We used to use scotch tape on dollar bills. Fold two lengths of scotch tape in half to form two "ribbons" about 12" long, and at the ends, tape them to the end of a dollar bill, so you have a dollar bill with two "ribbons" of tape hanging off of the end. Fold the tape in half, fold it over a dollar, and it fits in a wallet like any other bill, however, you go to a vending machine, put in your dollar, get yer coke/snack, pull the dollar back out of the machine via the tape. Free cokes and snacks galore. You can usually get like 15-20 uses out of a buck before it wears out from being pulled in and out of a machine.