This barely qualifies as a hobby, but at some point I decided to learn how to count in binary on my fingers. It’s handy if you need to hold a number in your head for a bit and can’t write things down, or to count past 10 visually on your fingers for somebody. There are probably YouTube videos on it. I literally can’t remember where I learned, but I practiced a lot when bored in church. It’s relatively non-disruptive and practicing can eat a decent amount of time.
0 materials. Just takes time. Literally free.
I did the same when Masahiro Sakurai explained how to do so when revealing Byleth for Smash Bros. Ultimate. It’s come in handy a few times when needing to count things out, and honestly can be a fun exercise for dexterity to just count to 31 on each hand.
It’s not free, but you have to pay for it no matter what, so it kinda is, but cooking. Everyone should learn the basics of navigating a kitchen and the basic terminology.
Singing and dancing are both learnable free. Art in general tends to be cheaper. Usually anyway.
Intellectual skills are all fair game, there’s wide availability online. You need to start with Information Literacy though, to kinda unlock the rest. Otherwise you’ll waste too much time on bullshit.
