Under-18s, with parental permission you may also be able to volunteer for a local campaign office helping them with things like stuffing envelopes and making flyers and handing out buttons. Not the most exciting work, but it makes a difference, especially for Congressional candidates in presidential election years. Often presidential campaign offices have lots of people since so much spotlight is put on that race, but a few extra hands at a Congressional candidate’s office is often very appreciated.
You might also consider, if you have a car, offering to drive people to their polling place on election day to help hold them accountable to get out and vote. I once “tricked” my friend into voting by inviting them to go with me to lunch, but after picking them up I drove them to their polling place and informing them that they weren’t allowed to eat lunch until they voted. A little devious, I admit, but it’s effective (as a point of reference, our school district gave students election day off, as all the schools in the district served as polling places and they were (unfoundedly) worried about “strangers” intermingling with students). If you can’t drive, bother the people in your life who are old enough to vote all day until they give you proof they voted. Maybe try to ignite a selfie competition of people with their “I Voted” stickers on your social media. Get creative!