You hear a bit about them being hard to feed, but this is mostly in planted, snail populated tanks where they don't need any additional food.
Before I moved mine into the 38 gallon, she was stealing the flake food I fed the Danios (and wow is she quick when she wants to be..)!
She's a huge HUGE fan of bloodworms, and also ate Tubifex.
I hear they'll also eat mysid shrimp, krill, glass worms, brine shrimp, and daphnia, but I have not experimented with these.
For snails, pest snails work well - I use Ramshorn snails (heck, you can breed these at home in a half gallon jar). It's important not to feed Malaysian Trumpet Snails, as I've heard their shells are too hard. One accidentally got into my tank a while back, and the Puffer just ignored it as far as I can tell, but why take chances when they're not needed? Ramshorns are cheap gotten off of eBay, and free at most chain stores and
LFS.