If your dog is normally fed kibble out of a bag, that is what he should eat -
sudden changes in diet can cause stomach upset - he could end up with gas, and die of bloat, or he could have diarrhea.
If you ave simply run out of food, 1/2 cup of rice with an ounce or two of boiled chicken will probably be fine - but I wouldn't go crazy adding anything else.
Make sure anything you give him is fully cooked through, and make sure the rice is extra mushy. You don't want it to form a brick in his intestines, either - but really, he would be far better off with regular dog food unless there is a very good reason to give him something else.