Comic books. I started with Moon Knight then went: Gambit, West Coast Avengers, and most recently Suicide Squad. I'm peeking into the vastness of Batman, X-Men, Avengers, and Teen Titans but that's a TON of comics to collect.
Like most people I used to collect Pok?mon cards, and I went through a short lived comic book phase. (I still love comics but they're just too expensive in the long run.) I have around 30 Sega Megadrive games from when that was a thing, and I'm thinking of collecting more of those. But right now I'm not currently collecting anything.
Nightmare before Christmas anything. My husband collects pez. And we both collect magic the gathering trading cards, although the we haven't bought any in a while.
Tolkien books hah. I have a little collection going on the top shelf of my bookcase. Probably have 10 or so different ones. My favourites are the 1974 Allen & Unwin editions of LotR that were my mum's.
I started collecting things at a young age and it apparently were rocks. I still don't understand what I wanted with cool rocks I'd find in the woods or in my yard but then it moved to Yugioh cards. Though now a days I'm collecting either Video games or merchandise to fandoms that I'm currently in.
interesting vintage clothing that i don't actually wear, BOOKS (i have a lot and many different kinds that fill my bookshelves), other kinds of random vintage things, video games and consoles, computer and electronic crap
perfume bottles and stickers
i must have about 50 full sticker albums in my bedroom, i was obsessed when i was younger and still can't resist buying a good pack of stickers if i see one in like urban outfitters or something
my ceiling/laptop/cello case are absolutely covered in stickers haha