I don't use a planner per se for my writing...although I have dozens of little pieces of paper, cardboard, napkins, post-its that I'd scribbled down ideas and outlines on.

But I do sometimes use a Kanban board I made and I have a binder that has page covers I put all my smaller pieces of paper in so I don't loose them.
Taking this picture reminded me it's sitting unfinished from when I started setting it up for Q4 of 2024. I should work on it and get my brain ready for my 2025 goals.