OK, I know what you're thinking — maybe you're not a writer. However, as Tamez says above, chances are, you're an expert sy ~something~. Also, chances are that other people want to know what you know. So whether you write an eBook on dating or tips on how to fix your car, once you write, self-publish the book, and let it go, it can sit on a site like Amazon and sell itself. Of course, you can market it, too, but that's another story! Some sites let you keep most of the earnings, while others do not.
Most of us think of investment income as just the cash flow we get from bank interest, bonds, share dividends and property rents, some of which comes via a super pension.  But a more complete view is to also consider how growing the value of your investments can add to your spending potential.  This total return approach generates income from both income and growth to optimise spending from your portfolio across all market cycles, aligning cheap and expensive investments to your goals.