That's actually a really tough question, mostly because it's hard for me to think of powers that are useless. I guess I would say the ability to smell like whatever I want. And I guess that's useless because there are already ways to do that!
Lack of education. I would make sure that people are educated and informed about the world, because that would fix everything else. All of the problems of society stem from a lack of understanding of others, their backgrounds, our -own- backgrounds, or the importance of knowledge and using it to make sound decisions.
Not to say everyone would go to college or anything, but you can get a great education in high school if your school isn't shitty.
Mmmmh If you could fix ONE problem in the world what it would be?
Not to say everyone would go to college or anything, but you can get a great education in high school if your school isn't shitty.