I mention this often here, but I think substitute teaching is the perfect FIRE job. As long as you don't accept a long-term gig, you are basically committing to nothing. If they call you the night before or morning of, you simply say no if you don't want to work. if you are going to be traveling or otherwise occupied for a window of time, you take yourself off the list. If you have pottery on Wednesday and yoga on Thursdays, you take those off your availability entirely. Pay isn't great, but it's better than retail/minimum wage. And if you are decent at your job, over time you can establish yourself and probably work as much as you want via requests.
If you live close to more than one school district, you can register at two or three to increase your odds of getting work. If there are schools in the district that are too far away, you can not take jobs there. You can also register at private schools.
Qualifications vary by location.
The downside is that it isn't especially reliable, especially at first and if you don't work enough to get requested, or if you aren't very good at your job. You can pretty much rely on having *some* income, but it's not like a job where you are scheduled for 20 hours a week and can then rely on having that amount coming in. So if you want/need $15k/yr and will freak out if you don't hit that number, it may not be the right fit. If, on the other hand, you just want some supplemental income, it's pretty perfect.