I bought a huge roll of black felt and sewed it into my rack curtains; I think next time I PCS I'm gonna gift my felted curtains to someone and just buy a Rack Pack (does r/Navy have any opinions on them?)
As far as personal comfort goes:
An excessive amount of audiobooks, digital books, hardcopy books, and music/movies. But mainly, the books. And seriously, audiobooks, I can read while working, it's tripled my reading time, and I already read a lot. Audible.com I have found to be worth every penny (especially if you get the sync-with-kindle ones so you can flip back and forth from reading to listening)
a very nice flashlight
a very nice pen (or two, and I always get a kind with a removable cap so when I lend it to someone I keep the cap so my pens don't disappear) and a Leuchtturm 1917; far better than a moleskin and I would be so lost without a notebook because I've got too much stuff going on in my work centers to keep track of by memory alone
an eye mask because I don't like being woken up by jerks who flick on the lights in berthing. I try to find funny ones like my zombie one.
Paint markers
a hard drive
An extra set of boots so I can switch out every other day and not get funky smelling boots
extra headphones and chargers, also this last float I bought a little portable bluetooth speaker thingie and that was pretty awesome.
High end body wash/facial cleanser/face masks; r/skincareaddiction or whatever that sub is always has good suggestions. It's my ten minutes out of the day to just pamper myself and I do it in style. Plus, when I've been welding or dealing with VCHT sometimes I just want to feel clean and fresh.
A sewing machine and extra rank and warfare devices, enough to sell/gift as necessary after advancement results. My FCPOA did a sewing fundraiser (fixing uniforms and sewing patches on) last underway and we made about 500 for a few hours camping out on the mess decks. When I was a fireman it was a nice source of income for me; now it is a constant supply of snacks for my shop (go get everyone in the shop some cokes and some chips from the ship's store and I'll have your patches done by the time you come back")