You can simply use them to pay in a supermarket or anywhere else. Just give them the card and say ‘put 1.23$ on this one please, and the rest I pay cash‘ or whatever. They might be annoyed when you have really many, but you can use up one every time you shop easily.
For some cards, you do not even have to know the remaining amount, just say use it up.
Note that supermarkets are preferable because they are typically used to that, and know how to handle it.