What is the base food you are using? IF it is really good you might not need to mix it up too much with other treats.

I'm with a couple of the others on the earthworms. My big fish just eat the things whole and my smaller fish get them chopped. All my fish go crackers for them and the best thing about them is they are easy to get from my worm heap, which I feed with grass cuttings and household scraps etc, and they are free!