Entirely seriously, learn how to make a game in Godot.

Its literally completely free, only costs you time, and assumes you have at least some kind of existing computer, doesn't need to be a monster rig.

Alternatively: Find a video game you like.

Make mods for it.

Here's another one that's basically free:

Becoming/Staying fit, gaining strength and agility.

Make 'weights' out of milk jugs with water in them.

Maybe get a resistance band or two, they're not that pricey.

You can absolutely do a ton of stretches, calisthenics, and light to modetate muscle group workouts with basically just random shit lying around a typical home or apartment.

You can find basic guides for these excercises often just freely available from reputable medical organizations.

You can literally just go on a 20 minute walk, 3 times a week, and be in better physical shape than something like half of the US adult population.

Back to computer shit:

Blender is free.

Learn 3D modelling, rigging, UV wrapping, how texturing works, how to make animations, etc.

Same with Krita.

Become artist. Draw stuff good.

You can find probably literally millions of free tutorials for how to do basic and intermediate level concepts.

Whsitling/Singing/Voice Acting.

These are developable skills much more so than they are just... things you either can or cannot do, for some reason.

You can teach yourself how to do these, again to a basic or intermediate level, for pretty much free.

Same thing with at least some kinds of dancing.

If you're feeling more EXTREME: Parkour and/or Urbex.

Lockpicking.

Go find the Lockpicking Lawyer on youtube.

Pretty sure he can recommend you a not too pricey basic starter kit for learning the basics.

... I could go on, but my hands are tired from what I'm going to call 'autism posting', one of my totally free, personal hobbies that I often indulge in.