small superworms (easy to breed, though it takes awhile so you may want to just buy smalls initially)
small roaches or the nymphs of larger roaches
small silkworms (easy to breed, though it takes awhile so you may want to just buy smalls or eggs initially)
small terrestrial isopods (easy to breed, though it takes awhile)
small butterworms (not to breed, just to buy)