I've long been drawn to the passive income supplied by creating an ebook and publishing an accompanied print-on-demand paperback. By using platforms like KDP and CreateSpace, both by Amazon, you can create an easily create and sell an ebook that costs nothing to produce, and a paperback that earns you money only when it sells, removing much of the prior friction it took to get published.
First, decide the composition of your target audience. Are you going to focus on aging skin-care products, or cosmetics for teens and tweens? Do you want to hit the burgeoning natural product market? Once you have a sense of who you are selling to, you will need to decide if you want to make your own products, or work and receive commission from a larger company.
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.