Do you have some knowledge, information, know some 'secrets', hints and tips, great gluten-free recipes, good websites/blogs/social media sites/forums, etc. which may be valuable to others, then why not write some eBooks. Although I sell an eBook called 'How to make $1000 a month from the internet' for just $3 in my eBook store, I am going to show you how easy it is to sell eBooks world-wide for absolutely no cost and very little effort once it has been written and is set up for sale.
The great thing about eBooks is that it is passive selling. Once it is available for sale you just sit back - everything (sales, delivery, payment) is automatic and it is very simple to set up too!
If eBooks aren't your thing, musicians can sell their own music files, photographers can sell their photos and artists can sell their graphics downloads. You can make and sell courses and coaching products on a subscription basis too (typically using Zoom, setting milestones, etc.).