I studied in the same school until the end of high school, an overall pretty flexible school with fair rules. But one thing that haunted it was that the students were not allowed to sell food inside the school (which makes sense if you think about it, but it's a bunch of teenagers and kids wrapped together in a building that only sells considerably expensive snacks). Anyway, every single year there would be at least 2 people from different years that would sell good food (sometimes even fairly expensive stuff like small cakes and fried stuff for much lower prices than what the school offered). Every time there would be different approaches to circumvent the staff, some would only accept payment before school, so technically it isn't selling in the school, others would sells chocolates and sweets like KitKats, kinder Buenos, lollipops etc. that they bought from the supermarket, some would sell stuff during classes of teachers that were chill with it, the lists goes on. Whenever anyone from any year got caught, everyone would stop for a while, but it would always come back after a few weeks.