Here's something kind of silly that I do: I keep a running list of ideas in a discord channel, on a discord server that's only me and a handful of bots. I've been doing this for two and a half years, now. Though some of the ideas are more pie-in-the-sky than others, it's a habit that I'm really glad I got started, because it's one of the foundations for the way I like to interact with the world — I love just sort of running around, doing little things that I think are cool, and the idea pile is a great interface for doing that.
Almost everything I work on outside of work starts off as something from the ideas pile. This can be as simple as the Series interface for javascript generators, to things that become a seriously large part of my life, like the cloud-first framework I'm working on, or the recurring writing projects I'm currently working on.
I also love to work by just sort of thinking about things until the way to go about them is so obvious that I just want to take the time to sit down and knock it all out. I love it when, by the time I actually start writing code, the application is already essentially written in my head, and the rest of the work is just a simple matter of programming.
Every day, I write 750 words in a journal, which I mostly use to kind of organize my thoughts about the past and the future. I have a command line tool, idea, which just grabs a random item from the ideas pile, and when I end up running out of things to write, I'll run that command and then write a little bit about the idea: how feasible it would be to do right now, how I would go about doing it, when I could actually do it, and the why of it all. And by keeping these potential projects fresh in my mind, they all sort of mix around and build off of each other, where fun things to do beget other fun things to do.