Replying to Shopping online if you are under 18

I got away with just giving my parents the cash and using their accounts before but if the item I need isn't absolutely necessary like christmas presents and stuff, they won't let me get it. My town has a dollar general and that's it so I can't just walk to the mall to get the stuff I need. I have a bank account with plenty of money but I can't use it because teens have zero rights when it comes to shopping online, so I was wondering if you guys know a way around it.