Snails will eat just about anything that makes it to the bottom of the tank. And even things that don't. I find my snails (1 gold, 1 black mystery) sometimes come to the waterline to eat food from the top of the tank. Especially when I am feeding Tetra Delica foods. I squeeze out a bit for them to munch on. So, in short, any food that gets to the bottom of the tank, that isn't eated by the fish will be eaten by the snails. Of course, provide them with variety just like your fish. I feed mine the Delica, shrimp pellets, algae wafers, frozen bloodworms, flake, lettuce, tropical sinking pellets and the occassional zuchinni.
\Dan