I have several suggestions. First is selling plasma (yeah I know this sounds weird) but unlike whole blood plasma can be sold for about $40 dollars which takes about an hour or so and since your body replenishes this much quicker you can donate twice a week. I personally have never done this but I've heard people doing it and researched it somewhat. I didn't really find anything terrible about it (can possibly make $300+ a month extra for minimum commitment). Another thing is tutoring. I worked as a tutor before medical school getting paid $25-$35 an hour. This job requires no capital. You can advertise yourself online (Wyzant, Craigslist, etc.) and you are free to schedule it any way you want and work as little or as much as your study schedule permits you. I'm sure there are plenty of college (especially nursing students) who are searching for tutors in science classes (biology, anatomy, physiology, biochemistry etc.) in your area. College courses are less intensive and much easier than their medical school counterparts so you don't really need to review before each tutoring session. Plus teaching it to someone helps you retain that knowledge.