If you will get yourself a cloth bag and put bread or fish chow in it, it will draw the bream and gills into the trap. By putting your bait in a cloth bag it will last longer. The gills and bream come up to the bag and suck on it to get some of the bait.
All the above work great. I usually use bread with a couple pieces of onion, not sure why but I usually get more that way.
Also, I've heard of people using packing styrofoam peanuts, Ramen noodles(which do work) and plain ol dry dog/cat food.
i had dog food in one and soured grain in the other out in my tanks last night, caught 10 gills in the soured grain and none in the dog food. Usually catch alot with dog food but i dunno what the deal was. I switched the baits in the traps to see if location had more to do with it