Any kind of food that wasn't homemade. Class trips.
At school we usually had a class trip to watch a movie or go to a museum located in one of the "bigger cities" once a year. I always felt pretty bad about the trip fee alone, but mom always insisted on me going since everyone else went and she hated admitting we were so poor I shouldn't go in the first place. After the main event of the trip, teachers always took us to a shopping mall so we could eat something in the food area - mom usually gave me equivalent of $5.
When I was younger, I'd get a Happy Meal, then trade the contents a bit with a friend - I hated fries, loved chicken nuggets, she hated chicken nuggets, loved fries. So she always gave me her nuggets, I gave her my fries. Yes, could've just gotten nuggets alone and it'd be cheaper and more efficient, but as a child I really, really wanted the toys included, they were a luxury too (once my older cousin gave me a small dog plushie she got with her Happy Meal and I kept asking her if it's really OK for her to give me something SO NICE like that). Remaining money I'd give back to my mom after the trip. She didn't ask for it, but I'd feel bad keeping it.
When I got older, I'd just get the most filling thing I could get for the cheapest price possible. Then return the rest after the trip. When we were in middle school, teachers started giving us "free time" in the shopping mall. We had to promise we'd eat, but other than that, we were free to roam around as we wanted. A lot of girls would use the time to shop for clothes. I checked out many stores because I was bored, but I'd never buy anything. One time mom gave me $10 instead of the usual $5, because she heard from other girls' moms that their daughters buy clothes during the trips. I just did the usual that time though - bought food, returned the rest of the money. Said there wasn't anything I wanted there.