Every time someone mentions an interesting book, I make a note of it. Then a couple times a month, I go back through my notes, pop open a website that shall not be named, snag em all, throw them into calibre-web and sync them down to my ereader. I can get hours of enjoyment from a 1-2MB file, and I love that. Same for older cartridge-format game roms, a N64 rom is generally under 50MB and can keep me busy for days, an NES or GB ROM is usually smaller file size than a book, and some great old DOS games clock in at a handful of MB.
What other great bang-for-the-storage-buck stuff is out there that you enjoy?
I know it's not the subject of this question but... Why is storage space size your metric?
Do you take pleasure in knowing your good experience came in a small package? Or are you storage space starved for some reason and that's what guides your quest?
I was referring to Standard Def, but both are good and pretty light on space!
The most enjoyable passions IMHO is when you unleash your creativity. Write with emacs. Compose music with musescore. Draw with krita. Or, better yet, do it off the screen.
.mod files for music. 3-5mins+ of music a piece with a storage footprint in the KB range. Mostly free, tons available online. Check out Mod archive for an easy web interface or ZXTune if you're on android.
