The climber in me would like to do something with gravity. We've lost too many.
Aloha

If it were me, I'd want the ability to control friction. Talk about a physical law for nearly every superpower! If you could use a small amount of power to selectively alter the coefficient of friction on any object, you could make a lot of things happen.

I could stop bullets simply by increasing the coefficient of friction in the air around me. I could run incredibly fast simply by decreasing the coefficient of friction in air (but not on my shoes)! As long as I had a method of propulsion, I could simulate Bernoulli's principle and create flight. The possibilities go on indefinitely!

Not sure if this fits but I would like to see people's moods. I would like to look at someone and see instantly if they are good or evil, happy or sad etc...I am not very good at that.