The best kind is called Lab Blocks. Make sure that your rat or mouse always has a bowl full of food that's made just for them. Special Treats Rats and mice love special treats. Just remember, rats and mice have little tiny tummies. Don't give them too many treats, it'll spoil their dinner.
Fruit is a great treat.
Rats and mice love to eat apples, bananas, peaches, strawberries, and grapes. They also love vegetables like carrots, celery, cucumbers, beans, and broccoli. Rats and mice love to eat lots of other things too. Spaghetti noodles with sauce, pizza crust, wheat bread, and even healthy breakfast cereal. Anything that's good for you to eat is probably good for your critter too.