Timothy hay cubes: They won't eat em. Trust me.

Dog Food: Pedigree is fine. Does your pet store sell Innova? That is the best to get. Nutro is pretty good too.

Crickets: Yes, they can have them. Canned or alive. My rat Nugget used to eat them alive.

Mealworms: Yep, just hand them to the rats. They will gobble them down. I have never met a rat that hated mealworms. Mine are little piggies when it comes to mealworms.