Food for aquarium fish is also quite suitable for feeding land snails and slugs. This was already mentioned in my chapter on raising snails in the book The Mollusks, edited by Sturm, Pearce and Valdés.
Here is a juvenile Triodopsis eating a piece of goldfish flake. The white stuff on the flakes and on the snail's shell is powdered limestone that I also give to my snails.
And here is a closer look. The snail's mouth is at the front of its head towards the bottom. You can see a strip of flake disappearing in its mouth.
Probably any brand of food for aquarium fish would be satisfactory for snails. The one I use is for goldfish. The first 3 ingredients in it are wheat flour, fish meal and brewers yeast, all of which are suitable for feeding to terrestrial mollusks. Most of them don't normally encounter dead fish in their habitats, but many appear to be omnivorous and eat dead animals as well as animal byproducts.