Writing an eBook, like you said, is not easy. First you have to have something to write about, which often means that you need to be some kind of respected expert in the field you wish to write about.However, if you can get past the initial trouble of selecting a topic, becoming an expert, and finally writing about that topic, that’s when the hard part really starts….
I’ve tried a fair few things on this list and I’m a big fan of those side hustles that have the potential for ongoing passive income once you’re set up. For me, the most successful have been blogging and T shirt designs (I use Merch by Amazon but want to look into Teespring as you suggest). I’m currently working on an Etsy printable business, again for the passive income potential!
With just a few paint and stencil supplies you could walk the neighborhoods with curbs and solicit your curb number painting services. Obviously, you need to be somewhat handy with a can of spray paint and stencils, otherwise, you might have people coming after you if you mess up their curb. However, there is a business for this as people are out there making it happen.

2. InboxDollars – InboxDollars is similar to Swagbucks, since you’re going to be taking surveys, shopping, etc., so if you want to maximize your return, sign up with both websites. They also offer a search engine that pays you (like Swagbucks) and you get $5 just for signing up.  I won’t continue to list survey sites one after another down the list, but if you want to get paid to take surveys, also check out GlobalTestMarket, E-Poll Surveys and Survey Club.