My girl rats were always picky. They'd eat the bigger stuff and leave the smaller seeds and green pellets in the rat mix. So I'd inspect every bag of every food at the store and buy whichever one had the least small stuff. I mized in a small amount of parrot food, because they like all the big pieces. They like the rat/mouse blocks, so they get added, too.
Not the healthiest, I know. But I was throwing away so much food that it was gtting expensive to feed them. Now that I only have Milo left, I'm not sure what I'll buy, once the stuff we have now runs out.