It's best to feed rats the commercial mixes made specifically for them. They are available in most pet shops. You can add a variety of fruits and vegetables along with cooked meat, bread, yogurt, small dog biscuits and more. Keep portions to about a teaspoonful . Some of the foods you shouldn't feed are highly spiced foods, sugary foods, anything that contains caffeine, carbonated beverages or dried corn. Always check food for freshness.