You can buy special foods for the crickets, to keep them hydrated and from starving. However, I'd only recommend those foods that keep them from starving. I just use oats to feed them, with the occasional carrot and lettuce.

Flukers cricket quencher can work magic, well, any cricket quencher can. I used only wet lettuce and oats before, but my crickets died pretty fast. Once I got the cricket quencher, they lasted 2x as long.