I don't get it.
I don't either. During my entire public school career, from the mid 1950s to the late '60s, I brown bagged my lunch. Never ate in the cafeteria. Bologna and peanut butter sandwiches, potato chips, Twinkies, etc. The only thing I ever bought at school were little cartons of milk or ice cream bars for 5 cents each.
Does anyone remember Shake-A-Pudding?