I would use super speed to squish grapes so good with my toes and make some good jelly.

To me, I always thought that it would be cool for a brainwashing ability to feed off of a person's insecurities. (As for why the ability wouldn't just take over the person's brain completely, I haven't come up with yet; perhaps it isn't initially strong to begin with, so it isn't able to fully brainwash people. But it gains power as the person it is used on slowly descends into madness) The more insecure a person is, the more the power takes over them, until they eventually become brainwashed altogether, leaving their humanity behind, and they become ready and willing to fight for the opposing side. It almost sounds like a Jojo Stand ability.

Using Super Speed to have a different job each day and be efficient at all of them. Like using it to power up a neighborhood, deliver Pizzas or other things, allow Nasa to test on you...