You can order a kids size meal at any quick-service restaurant, and noone will bat an eye.
Eat one large meal in the early afternoon and then spend the remainder of the day munching on snacks.
Bring snacks like cracker packs, mixed nuts, and string cheese to snack on through the day.
Ordering an adult-size entrée at the quick-service restaurants to split between a couple of people is another great way to save money.