Don't collect stuff.
For practical things, you can only use one thing at a time and maybe use one or two things as backups or spare parts. If something sits in a box because you don't use it, that's space you could be using for something else. The money you spent on that thing could be growing in an investment.
For decorative stuff, if it's on display, that's ok, but, like the practical things, if it's in a box, toss it into the trash or sell it (if you can quickly. Don't hold onto it forever thinking it has value).
For sentimental things that are useless, take a photo of it and then throw it away.
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Personally, since I am the youngest child of the family, I ended up with all the hand-me-down clothes and other stuff left behind when siblings moved out and didn't want the bulk (but still somewhat retained ownership of?). This has resulted in my owning basically every piece of clothing, every toy, every knick-knack, and every video game that my family has ever owned in 40+ years. Since moving out on my own several years ago, I left behind a lot of it at my parents' house, but I still have a considerable bunch of junk in my orbit that I have brought along for the ride. I have recently been going through my garage and attic and throwing away all the crap I've kept in boxes and bins since moving into my house, and last year I donated a ton of clothes I never wear. If something is difficult to throw away, I snap a photo before throwing it away. I'll probably never look at the pictures, but it, at least, satisfies any psychological hang-up I have. It also keeps a record of what I've thrown away if I ever go searching for it in the future and wonder where it is. There comes a point where the joy of being free of this crap and of having more space outweighs any joy keeping the stuff brings (or any anxiety getting rid of it brings).
A lot of stuff is still at my parents' house, and I have been throwing away a ton of that too. But then there comes the "collectible" stuff, like glass figurines and lamps and vases. This stuff probably isn't actually worth much, even to the right people, but I'm not sure if I should just throw it all away. This stuff never should have been collected in the first place. The only idea I have for it is to rent a booth at a local antique shop and sell it for dirt cheap until it's all gone. But even then, it would maybe yield a couple hundred bucks over the course of however many months it takes to sell them.
Anyway, don't collect stuff, even if it has a theme or hypothetical purpose. It just ends up being an anchor that you have to drag around with you wherever you go and that you have to store indefinitely. Yes, I'm a hypocrite, but that's the point. I know how it ends up and I'm trying to fix it and to say this as a warning.
Keyboards are definitely one of these things I am trying to whittle down to the essentials. In the past few months, I've been using one of my original mechanical keyboards almost exclusively (Quickfire TK I bought in 2013. It's just easier to move around and I don't care about scratching it, and I'm caring less and less about the minutiae of switch feel), so it makes an even greater case for downsizing. But selling these things is hard.
