People are always looking to have their cars washed and detailed. You could be a mobile car washer and detailer without having a permanent location. Reach out to people you know or make some flyers and put it in your neighbors' mailboxes. If you want to get serious about it, prop up a one-page website or give out business cards. You can make money quickly doing this.
Great list. I have another to add that’s almost as easy to do as going for a walk! Provide a litter cleanup service outside commercial properties for property management companies. The work is done on foot using simple hand tools. I started this service in 1981 as a side hustle and quickly grew it into a lucrative full-time business that I still operate. I share my experience with others in my book, Cleanlots, as well as offer free support.