I love journals, stationary and notebooks so I always have a ton because I think they're pretty, but then I end up not using them. I have used some in the past, though. I've kept a diary/journal off and on throughout my life. I have one from elementary school, one from middle school to early high school, and one from my 20's. I love to write down my thoughts and experiences to refer to later, especially for writing, but I can be very wordy and keeping a journal quickly becomes too time-consuming so I end up letting it slide until I just don't do it anymore.
I've also kept a writing journal dedicated completely to story ideas, inspiration, jotting down quick poems or phrases that come to mind that I know I'll want to use later.
Then, I have a few notebooks dedicated to different writing projects, but I would usually only jot down a character list or brief backstory and then the rest of the notebook was left empty. I only did an outline for a story once and I found I really didn't like it.
For a while, I was keeping a journal where I would write about recent books that I read. Basically, I would review them and write down my thoughts and impressions because I thought they could inspire me later.
I also used to keep journals at work for jotting down notes and to do items during meetings, but then I started having to bring my laptop into meetings and it was just easier to note things there. So I have all these journals at work now that I'll probably never use again.
It may sound like I've done a lot, but most of my journals only have a few pages filled in and the rest is blank. And I have a ton of completely blank journals just sitting around with no purpose at the moment.