Yeah, puffers are messy....they use that anal fin as a manure spreader for the most part so no luck trying to vacuum out the large dumps.
A good diet for puffers has variety. Some will eat green stuff but not all. Don't push it if they don't....that is what we have tangs for...j/k. By variety I like to feed one thing one night, and rotate. You can mix it all at once and do the same every night but as long as they get the variety they are good.
My puffer's menu includes the following: mysis shrimp (frozen), silversides (frozen), krill (mostly as a treat), fresh market shrimp (shell on), FM squid, FM mussels, FM scallops. I'll soak whatever I'm feeding in Marine C and Zoe. Also cut/chop foods to close to bite size as possible for the fish. Some will bite/chew up larger chunks and some will not...
Its actually much cheaper to buy this stuff fresh, freeze it, and thaw daily what you need. If you take a razor (or henckel 10" depending on quantity) and chop while still frozen it will A) thaw easier/more quickly and B) be easier to work with (will slice vs deform/stick)
To help reduce mess I find it helpful to take one of the fine mesh nets and rinse the frozen stuff first, then soak in supplements, then drain off excess. That way a minimum of "fug" gets in the tank that isn't eaten directly.
Happy Puffering...
