While tutoring students in traditional school subjects is always a viable option, there are endless possibilities that extend beyond schoolwork and children.
English (or any other language) as a second language
There are millions of people coming to the country who need help leaning English. As a native English speaker you can help, even if you’re not a formally trained language teacher.
Find a few people who are willing to pay you to teach them, and you’ll have a nice side business. Websites like Tutors.com can help hook you up with potential clients quickly.