Crackers, cookies, fruit pouches, granola bars, tuna pouches, raisins, applesauce cups, lots of fresh fruit (we drive), oatmeal, cereals, gatorade, and then small treats (mostly candy) as rewards for waiting in lines nicely.
I never go with a bag unless it have a zipper. Between being shoved under strollers or in rides, it always gets turned over. I would have to lose something.