My daughter, and many of her friends, all bring their own lunch because on average the cafeteria food sucks. the rules are even worse - they can purchase nothing a la carte, it’s an all or nothing deal. So if a kid ants a piece of fruit, they have to buy the entire lunch or no fruit.
Tell her it’s not always better at work. I got in the “brown-bagging it” habit when I was in school, and it’s come in handy ever since. I’m saving a fortune over the office cafeteria food. And mine tastes better, too.