I think this is a great way to present some other collectible hobbies on this forum!
As for me, I have, for a long time, collected the below (after also, of course, collecting stones and random gems and pebbles first).
- Original video game and different media (e.g. VHS covers, book illustrations, board game art) collection.
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I have about 10 pieces in total, but I think with the nature of the artworks (everything being 1:1) and the prices, this is still quite a lot for me (although as we know, there are always collectors with hundreds of pieces, regardless of the hobby).
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Here is my personal grail, that I believe I will never get myself to sell. This is the original artwork for the box art of a Tom & Jerry GBC game. This is a fairly random game but it was the first ever game I played and myself owned. It was a gift from my parents and I used to play this for years, never beating it, when I There will never be anything more nostalgic to me than the soundtrack in this game.
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Here is also an original tile illustration from my favourite boardgame Tigris & Euphrates.
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Spawn: Armaggedon Story board artwork:
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Video Games - I have one graded copy for memory and then many CIB ones. I love Gameboy, Gamecube, and N64 mainly.
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Paper notes - inherited from my grandpa, who inherited it from his dad who worked in a bank, and was able to obtain some great-condition notes from as much as 100 years ago. Here is one in a great condition:
- BOOKS
- I do not buy them for collectible purposes but if possible, I like to buy a physical copy even if the book is rather old (the same goes for some academia books, old manuals and so on). I think this is a very common collection people have without realising it, as books also hold some good value (although I do appreciate that collecting isn’t inherently connected to monetary value of things!).
- MTG - I love Arabian Nights, the best TCG set ever!!! (totally unbiased).
Why?
I enjoy the idea of preserving things, as well as appreciating that things can carry a sentimental value. In this regard, I am as opposite of a minimalist in this regard as much as can be. Is this called hedonism? 
Luckily, I am not yet in the ‘hoarder’ territory.
I also really enjoy the parallels and differences between hobbies, seeing how the markets move, how discourses shift, how people enter and leave the hobby and so on.
Nonetheless, I also hold the (maybe controversial) opinion that caring about value of items, is a big part of collecting, at least for me, and I do not think it is bad.
A lot of the stuff I purchase I would not have bought if I believed its value would drop. I would not buy a card worth hundreds (let alone thousands) knowing that I am essentially throwing my money away without means of regaining it (or part of it) again (by selling). Maybe this is because the money I put into it is often still of significant value to me. But regardless, there are also pieces I would never sell even if their value increased 10 fold from where it is now.