What to do with extra guppy fry?

If they are small enough to be eaten by your other fish, place them in your main community tank. For example, angelfish are always delighted to reduce your guppy fry population. If you do not have any other fish and they are too big to be eaten by their parents, then I would suggest giving them away. Some pet stores will give you in store credit if you exchange your guppies with them for in store credit-not all stores will, but you can always call/email your local pet stores to find out. If your pet stores do not offer such an option, I would give them away via Craigslist, friends, et cetera or just keeping them, if you have enough space. However, if you don't have adequate room and equipment to keep your guppy fry, I would highly suggest checking with your local pet stores, feeding them to other fish, or as a last resort, giving them away.