I would teach someone some basic phrases of a foreign language and hand them a summary sheet as well. I still remember how to count to ten in Spanish from when a visitor from Spain came into my kindergarten class. Or teach them the basics of CPR if you are recently certified. Or similarly, how to calm a victim in shock (wrap them in a blanket, comfort them, etc), which requires no training unlike real CPR. I would shy away from crafts because those require items to complete, and can be complex enough to be forgotten within a few days of practice (such as knitting). I also feel that knowledge that requires no items is handier than knowledge that requires items, which is why I would focus on sharing knowledge that requires no tools.