Since I'm involved in that other gutload thread I'll just keep going here..
Collard greens and mustard greens, and a high calcium dry feed. Sometimes other table scraps like carrots. A recent study my herp vet told me about said that chicken scratch is really good, higher in calcium then most dry gutloads, and cheaper. I haven't tried it yet but I probably will. Do some research first.
If you keep them in a container with food over a 24 hour period (or less) I would take a guess that you can count on the fact that almost every cricket in that container has had a bite to eat. If they're crapping green dots around their container (more noticebale on eggs cartons) then they're loaded.