Renting Rooms
We've made tens of thousands of dollars over the years renting out bedrooms, even when we were living in a mobile home at the time. We charged a weekly rate that included all utilities, making it very convenient for students and single people. I've also known of people renting a spot in the yard to somebody to park their R.V. and live in it. I once converted a shed into a bedroom and rented that out too.
Rummage Sales
Find everything you don't need (maybe half of your possessions) and have a sale. We find it better to simply take it to a flea market. The fee for a spot is usually cheaper than an ad in the paper and you are guaranteed some customers if it's a good flea market. If you enjoy the process, you can start accumulating more stuff to do it all over again.
Closet Grocery Store
I used to make a little money running a "grocery store" out of two shelves in a living room closet. My room renters paid regular retail for cereal, soup, etc., which I would buy during half-price sales. Also, selling cold pop out of the refrigerator for 50 cents was a regular source of income for years.