Teach someone considerably older than you how to do something (anything) on a computer.
I helped a friend from my former department learn how to select a default printer since they did a system update that wiped everyone's personal settings. I showed him the steps and told him what I was doing as I did it. We repeated the process a few times, then I typed up the step-by-step instructions in a Word document for him.
I did similar things for my grandmother when she was still alive. She always had a topic for me when I came over to visit, usually something simple like attaching a file to an email or saving documents to a specific folder (then locating that folder at a later time). So I would show her several times, then have her show me how to do it, then I would write up a quick reference how-to in a spiral notebook that she kept on the desk. It seemed to help a bit, although the process with her took much much longer than it did with my work buddy.
My friend and another member of the old department came up to me today to thank me. He was able to show her how to add printers by using my instructions that I had left for him. I was delighted to hear that. I'm usually awful at teaching anyone anything because I have difficulty explaining things clearly and get impatient with it. But it was nice to be able to teach someone effectively, even if it was really basic stuff.