- Make things that solve problems you have.
- Make things that seem interesting/fun to you.
Borrowing ideas from other people seems unlikely to be very engaging, and making things just to learn skills has the same problem.
Lacking side project ideas seems kind of incomprehensible to me, as I have far more ideas than I could ever put into practice, even if I didn't need to work for a living. Therefore, I suspect you do have suitable ideas, but maybe aren't recognising them as such for some reason?
Scripting repetitive or annoying things is an easy place to start. Maybe start with simple website-improver GreaseMonkey scripts, to fix things that bug you, or make your life easier?