I think you should get busy pursuing your interests, even if you are a senior. It’s never too late to show some enthusiasm. You can always volunteer around town because volunteering really makes everyone happy; it’s a win-win. You help people who really need some help, and it brings you joy. We have a great list of places to volunteer in our Resources section, under Volunteering!
You could also get a part time job, or even start a company, such as walking dogs. If you like to create websites or phone apps you could do something creative, like make the world’s first dating app for dogs, where bored dogs could make friends to go on walks and playdates with. You could call it Lonely Labradors, or something else that would obviously appeal to all of those canine iphone users. 🙂
Don’t forget that listing things like hobbies (reading, hiking, fishing, etc) is totally fine on the common app, and certainly list any family responsibilities that you may have, such as caring for younger siblings. And if you create things like woodworking or poetry or sewing, certainly list that.
And one other idea that comes to mind is to find a way to mentor younger kids, through sports or tutoring at the local elementary school. Go back to your former teachers and offer your services. Those people know you and can put you to work decorating bulletin boards, running errands, photocopying, etc and possibly tutoring.
I hope this helps!