Rare/Old/Foreign Currency: If collecting money wasn't so expensive I'd totally go for it, but I have to be lucky to find them. So far I have a few Canadian quarters, a Barbados quarter, a 10 pence coin, a bunch of $2 bills and this giant $1 coin that doesn't fit in any vending machine.
Abandoned Businesses/Homes/Parks: There's just something eerie and fascinating about wondering about what was once there and what happened to it. There's a guy on YouTube named This Is Dan Bell who makes videos about dying and dead malls. It's so weird how not too long ago these places were lively.
Old Technology: Any doodad that I grew up with or older is cool. I like looking through old department store catalogs and looking at how different things were back then. I went to a store that sold all kinds of old stuff like rotary phones, typewriters, etc and I deeply regret not buying anything. Although they'd be collecting dust on the shelf. I don't think old things were better, just fascinating. I definitely wouldn't downgrade my Windows 10 laptop to Windows 95.