Preheat oven to 325 degrees F. In a large bowl stir together brown sugar, ketchup, salsa, barbecue sauce, mustard, and steak seasoning. Stir in pork and beans, butter beans, kidney beans, and onion. Transfer bean mixture to a lightly greased 2-1/2- to 3-quart casserole.
Cover and bake for 1 hour. Uncover beans and stir. Bake, uncovered, about 45 minutes more or until desired consistency, stirring occasionally. (Beans will thicken slightly as they cool.) If desired, top with broken potato chips.