For my "mini" monsters (Hogchokers) I generally feed earthworms and occasionally Hikari carnivore pellets. More importantly (I think) is that I have mollies and ghost shrimp breeding in the tank. While I have only seen one molly fry eaten by a hogchoker, I currently have no molly fry. When I was first transitioning the tank to brackish I had snails as well (and I saw a hogchoker sucking on a snail once) but now my only snails are zebra neuritis and they're way too big for my fish to eat.
I like the idea of constantly growing more feeder fish (or shrimp) in the tank with the hogchokers. I realize this would be impractical with larger predators.
On a side note: I went several months without seeing one of my hog chokers eat an earthworm (I think, hard to tell the apart when they're buried in the sand). I assume it was feeding off the occasional molly fry.
Now when I finally get my dream tank/paludarium set up I'll have to figure out a way to keep crickets gut loaded in them for my mudskippers.
My mudskippers currently get crickets, Hikari carnivore pellets, flake food they dive into the water to get, and several types of frozen food (spiralina enriched brine shrimp, etc)