Unfortunately you're not going to get rich teaching, so many teachers decide to supplement their income. You can find loads of different jobs in the article I've written about offline jobs and online jobs for teachers. All of these jobs tend to fall into 4 different categories and you can find those below.
Occasional Jobs
These are jobs that pop up every once is a while. Editing and testing are two good examples. You usually don't have to commit to that long of a time and can take a job here and there.
Seasonal jobs
Camp jobs fall into these category. They're intensive, but short-lived. If you can paste a smile on your face for 8-10 hours a day and do that for a week or so, then you're golden.
Part-time Jobs
These jobs require more commitment. Perhaps you'll tutor kids in the evening or work at a school on the weekend. This is money you can count on month after month.
Passive income
Making money while you sleep is the way to go. There are tons of ways to earn passive income and those range from blogging, to Youtube, to affiliate marketing, and even rental property. You need to find what works for you. Just don't quit your day job until you have a steady income stream. Everyone talks about passive income, but it's not as easy as it looks. If it were, everyone would be doing it.