Do two meals a day, instead of three. Eat small snacks to tide you over in between.
Split meals. The portions are usually really large, and you can't take leftovers anyways usually... I hate to see food wasted!
Dont order drinks and dessert and appetizers. THey add so much to a bill! Drink tap water, and grab a coke later on that you can drink on awhile. Or better, yet, stick with water in the parks. Desserts are wonderful at Disney, but expensive! Instead, have dessert later on as a snack someplace else. Portions are usually so big you dont need appetizers too.
Eat your big meal at lunch to save money, and a counter service or off property place for dinner
Dont be afraid to eat off property. While I love eating at the parks, or resorts, they usually are a bit higher priced. Nothing wrong with Chilis for dinner one night, or even Dennys!
Research all the menus ahead of time so you know what price range and such you're looking at... think ahead when planning your day as to where you might be at meal times and where you want to eat. So you dont waste time wandering to look at menus, and dont have to settle on something a bit more expensive because you didnt plan ahead...