While you may think that selling items in school is a good idea... it s not. Your school probably has rules against it and you could end up with detention, suspension, fines or other penalties. Forget about what to sell until you determine if you are allowed to sell anything and then treat it like a genuine business.
if you have a computer, then maybe you can consider doing dropship business with some online shops, like http://www.b2c-support.com, you sell things from them and gain the middle profit.
YOU COULD SELL SOME WEED!!na im playininstead of doing that GET A JOB (EX: mcdonalds, wendys, foodmarket