Become a teacher, preferably in an easy subject/grade level so as to take up as little of your spare time as possible.
All teachers have to do work in their spare time with grading/organizing assignments and lessons, but as a freshman health teacher (I'll admit it's a joke) I have ALOT less side work to do than the guys who teach advanced-level senior classes like Honors Calculus or Honors Chem and make the same money I do. I do almost no work outside of regular school hours, all grading is done during my prep/study hall block in school. I even have quite a bit of free time during school to look up coaching stuff or just browse the web.
So being a teacher is your basic income while you also coach. So to make extra money, look for something you can really focus on during the summer. There are countless things you can do. A fellow teacher/coach and I started up a jet ski rental/food vending operation at several very popular local summer hotspots. It's a simple gig and at this point I just hire kids to actually work the place while still being quite profitable.
Another teacher/coach owns a driving school, makes a sh*tload of money given the fact that he interacts with dozens of 15 year olds and their parents every day.
I invest my money pretty well and all told make close to 6 figures/year while living very easily.