I have many notebooks. They range from pocket sized to 8" x 5" when they’re for ideas. I’ll occasionally use larger ones for other things, but I want to take down my thoughts quickly, and I really only want the essence of them, so I write in references to other things, images, and a short phrase to title it for context

The nice thing is I’ve got almost 2 decades of notebooks like this - they’re scattered all through my things, basically by era.

And because of that, I don’t need to fill or organize notebooks - every few years I’ll see one I like and make it the idea book

I’ve gone through like 10x as many for work, but I just throw those away when they’re full