Quality dog and cat kibble, baby cereals, fish food (from catfish feed to tropical flakes and algae wafers). I've thrown random bread items and other grain products that go stale or won't be eaten in there as well. I'll also throw in misc things like Crested Gecko Diet or Bearded Dragon Rep-Cal pellets if I'm feeling froggy.

I used to grind up my food, and it probably makes their life easier because they can spend less time breaking down large chunks of food and spend more time breeding and doing other roachie things, but I've found that it isn't all that necessary. Cockroaches are pretty excellent decomposers and can handle much of what you throw in there. This is particularly true if you have a stable population, because adults can more readily break down larger chunks to make them accessible for the smallest of nymphs. Cockroaches are also surprisingly selective in what they eat if you offer a good variety regularly. For example, when I offer chick feed and dog kibble at once, the chick feed will usually be attacked second and they will leave behind much of the corn and cellulose base. If fed just the chick feed, they will eat the majority if not all of it.

I think the gutload recipe you've developed is pretty solid - just keep a decent rotation and variety of salad items going through there as an additional nutrient supplement and moisture source and you'll have some nutritionally-packed feeder roaches. Preferably avoid lettuces and the like with low nutrient densities and focus on dark leafy greens and other fruits and veggies.