What if your parents get you something for Christmas that you don't want?

I know this sounds horrible because I should be grateful. But there are a few presents under the tree for me and I didn't specify anything that I wanted and kind of just said that I want money this year because there's nothing at the moment that I want and I can use the money to buy whatever if I see something I like. But if I open them and I don't want them, I don't want to be rude or seem ungrateful but at the same time, I don't want to keep something that I'm not going to use. I would prefer they get their money back for something I don't really want.