Hi! finally something i know about.
These things ARE pests and WILL eat anything, however obviously not something with too much salt in it.
The tank should be pretty damp too, not damp as in make it humid, just damp.. like youd get under a rotten log. They are pests, but also detritivores.
I feed all my slimy things mostly cucumber and lettuce, and also bits of apple. Its kinda like a trial at the beginning to find out what they really like.
A favourite of my giant Achitina Fulica loves bread soaked in beer (believe it or not). They really enjoy a drop or too of beer, and make really random patterns on the tank, but only give them a drop, unless you want an alcoholic snail. (and obviously itd dry em out)
Some will also eat meats such as mince, for instance sometimes ive fed a snail a small piece of pizza, obviously with as little salt as possible.
I think i can attribute its very old age to its diet, cos according to some websites they are only supposed to last 5 years and mine is at least 10!