I'd love to be able to fold plain paper into all sorts of neat origami things. They don't even need to do anything, being able to leave an origami piggy on a neighbour's doorstep is more than awesome enough.
Even so, origami could have lots of wonderful uses. Origami pieces could be used as ingredients for decorative furniture, they could provide a small daily mood boost when gifted, origami cups could be used to make your own sno cones, and more!
Maybe you could even fold single-use tools for occasions where you get a barnacle stuck to your forehead and you left your scraper at home.
TL;DR: Origami.