Just about anything but FD krill...bad stuff, and what's worse, is once many fish get a taste for it, they will often refuse all other foods.
You should be feeding your puffer shell-on table shrimp, clams, mussels, snails, crab, and SW fish flesh (salmon, tuna, snapper, silversides, etc.). Feed appropriately-sized pieces, and if you keep the shell on, it will help keep the fish's teeth in good shape.
HTH