To get an idea of what I feed my rats look at this picture of their food. I also supplement this with fresh fruits and veggies such as apples (without the seeds, these are toxic!), collard greens, bananas, papaya, romain lettuce, mustard greens, broccili (sparingly as it can cause gas), cooked mushrooms, cilantro, carrots, green beans, frozen peas so they can "fish for them". I put them in water and let them go ratty fishing, it's one of their favorite pastimes.

Also I am sure I posted this link once but here it is again. What to feed your rats...