Other stuff you might consider adding to his kibble:
raw (or cooked) ground beef or ground turkey, chicken meat
canned fish--mackerel or sardines are great
frozen greenbeans, blueberries, squash--anything except corn and onions.
cooked sweet potato
or if you're really adventurous--
any kind of raw meaty bone--turkey neck, chicken wing, pork neck, etc. but only raw. no cooked bones ever.
You can also supplement his kibble with a good quality canned dog food. Buy a can of it and mix a few spoonfulls with the kibble--or mix the canned with some water to make a gravy.
If your goal is just to make the meal interesting, then none of these things has to be much--it's just a treat. A cup of anything is considerable, so you'll have to be conscious of the nutrion in that cup of stuff.
If your goal is to actually replace part of his kibble meal with other foods, then do some reading here and elsewhere on home-prepared diets for dogs and get an understanding of what makes a good dog diet, either in raw or cooked form.
I'm not so much on the rice---it's good if he's sick, but as a regular diet staple, I don't think it's adding too much except starchy calories.