What ways beyond the standard (background, RP, basic wiki) do you express things for your character? Do you do any to help you get into your character's head? Or any that are just for fun?
Additionally, what creative / inspirational methods have you found that work for you? What helps kickstart ideas? What helps organize ideas? If you're in a rut, creatively, what gets you out of it?
I've begun doing some aesthetic boards for myself and others. They fall squarely into the 'for fun' category. Been doing them here and there because, well, I've gotten to that point of the last few months of my degree where I'll hit a wall some days and just have to do something wildly different for a little while. There's an etsy store full of neat cross-stitch designs from a guy who did similar. Though his was initially an all-nighter of "design pixel cross-stitch instead of study!"
These are a Tumblr RP thing, I think? I'm guessing. I was introduced to the idea by a friend. She makes pretty awesome ones. I'm still kind of new to it.
But as an example, here's one I did for John Constantine on Gods & Monsters:

(You can see the others I did here.)
It's fun, relaxing, and so wildly different from the other stuff I do (work + school) that it's a really nice brain break. But it also helps me keep in the mindset of the characters I'm working on. I honestly might begin using them for stories I do moving forward because it could be used for characters, settings, scenes, plots... You could even expand and make them bigger.
Another thing I've done with my recent plot is break out Microsoft OneNote. I love the structure of it; haven't found a replacement I like (Evernote just doesn't do it for me, I'm afraid).
Anyway! I like that I can arrange things sort of like a physical scrap book. I have sections: notes, brain storming, a place to put logs, a place to put my summaries, a place to put NPC profiles, location profiles, etc. Instead of just a big GDoc or .txt file (the way I've usually done it!), I have this one thing I can just flip to and it's arranged more how I think rather than a big document I have to scroll through or a series of them open in multiple tabs. It's all self-contained in one program that's neatly organized and labeled.
I'm not sure I'd apply it to anything outside of plotting, but I really appreciate it for that purpose. Honestly, it's done wonders for me for organization as a tool. I highly recommend trying methods until you find one that really truly works. It's like going from 'yeah, I use this and it does the job but I don't enjoy it' to 'holy shit I actually have a passion for this again.'