First of all if you know that selling items is against policy, then I would not recommend you do it. The odds are your parents are paying for your catholic school education and it's not worth risking suspension or detention or whatever. You are responsible for the consequences. With that said, why don't you consider selling on Ebay (with parental approval and supervision) and then mentioning to students and teachers what kinds of things you have for sale, what your ID name is, and that local purchases will save on shipping by having items delivered by you. You will also be opening up to national sales, establishing a part-time business you can put on your resume when you get to that age, and make some nice money.