What do I feed my aquarium snails?

Okay I don't have any algae wafers or brine shrimp or any fish food at all. I've been given 2 aquarium snails that are very hungry. They are alone in a 5 gallon tank with no other plants or fish. So they have nothing to feed on, no algae as the tank is newly set up and clean. What can I feed them? Any food commonly found in the kitchen? (Lettuce, etc.) Please help, they are hungry :(