You know what I did to improve my finances as a medical student? I lived like a college student in terms of housing and I had a keen knowledge of which bars within walking distance had the best food and drink specials for any particular night of the week.
The most straight forward side hustle I employed during medical school was simply to work. For about 18 months, I kept my job as a research assistant and worked at nights and on weekends analyzing samples for about ½ of my full time salary.
There is tremendous demand for people with medical knowledge. This fact is easily demonstrated by the fact that I, a mere student, have served as the medical consultant for 3 different companies in the last 4 years.
Much has been said about affiliate, or niche sites as a vehicle for passive income. In short, you connect customers with suppliers of a product through reviews, articles, and links to those items.
Think of this like real-estate lite. You probably can scrape up the cash to buy an ATM. For 2-5k, you can be the proud owner of a middle of the road machine and depending on location, earning $200-400 per month through transaction fees.