Great list…a few are a bit humorous. Nevertheless, side money is still side money. An I am a firm believer that everyone should have something they do on the side. From my own personal experience, having something on the side helps takes the pressure of the main income source (both mentally and financially). If all you have is a single source of income, and if for whatever reason that source of income is threatened, the news is almost always devastating and life changing.
I surprisingly get a lot of people asking to detail their car. I never intend to make a business of it, but I love doing it to my cars and people ask me to do it to theirs. All it takes is a cheap orbital buffer (mines a used craftsman) and a shop vac. I normally get easily $100 for a basic wash/wax/vac, or $200 to remove scratches and polish then wax the car.