A Doane Paper Grid + Lines spiral book. This lives on my desk as scrap paper. Everything gets scribbled here, like doctor's appointments that need to be transferred into the planner, grocery lists, reminders, lists of which fish I still need to catch in Stardew Valley. Things that get written here are either transferred into another notebook later, or thrown away.
A Traveler's Company notebook system in passport size. This is where I jot down new story ideas, the starting lines of new drafts, or outlines before they get written into the Seven Seas. It's also where I take notes when my writer's group critiques my stories. It serves the same function as my novel planning notebooks, but for stories.
It's a lot, right? Maybe too many, but maybe not. It's a system that has evolved over decades and reflects my need to keep different areas of my life organized and compartmentalized. It also allows me to try lots of different notebooks so I can pass my thoughts onto all of you. I really do put all these through the wringer. You can even see some of them are starting to fall apart. But most of all, and most importantly, using this many notebooks lets me justify buying more notebooks.