Steve, we like grilled or quickly sauteed veggies in ours - zucchini, onion, peppers, eggplant, fennel, artichokes, asparagus, broccoli, corn, mushrooms (incl. portobellos), summer squash and tomatoes (dried &/or grilled). Also good is leftover tri-tip, steak, chicken, pork, cut into thin strips, shrimp (although I don't care much for seafood with cheese), salmon flakes, slices of jalapenos, a little salsa (we're partial to Muir Glen Organic Cilantro-Lime Salsa). I like cilantro, so usually add that too, + or - other herbs & seasonings.
Almost anything you like. Google for interesting combos too.
Have fun!
Rita