Shape-shifting to get unlimited free samples
If I had a magic flying broom, I would use it to do parcel delivery in a small, idyllic city somewhere.
Various superpowers: Generating free energy.
Psychological horror about the government taking all supers and putting them all in one giant box so they can use their powers to boil water. They all think it’s for the greater good. Plot twist is that it’s actually someone’s basement
Superman’s X-ray vision would be awfully useful for surgery. For that matter, X-ray vision plus precise heat-rays could maybe be tuned to vaporize tumors in-situ.
Spider-Man web formula would make for a strong, cheap and light substitute for almost all materials used today.