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 was referring to Standard Def, but both are good and pretty light on space!