First of all, make sure everything is unseasoned, unsalted, and mild. Avoid really rich or sugary foods, as well.
You can give him/her cooked chicken, beef, or cooked egg. You can also give raw or cooked carrots and broccoli, cooked rice (brown is better). Although these things aren't cooked, you can add a bit to your dog's meal - peanut butter (only a small spoonful), cottage cheese, unflavored yoghurt.