Personally, in addition to the media collection -- music in FLAC can take up quite a bit of space as my library continues to grow, and movies and such tend to be space hogs as well -- I keep a software archive for tools, games and drivers for everything I currently own. I fetch stuff as needed and just hold onto it indefinitely. Does that make me a digital hoarder? Maybe, but it's come in handy far too many times for me to stop. I already have a few things -- mostly old games -- that I archived shortly before they disappeared off the internet (save some far-flung reach of the Wayback machine, perhaps) forever. I also like to keep backup images of all of my machines so if I screw something up it's no big deal to restore the image so I hopefully don't have to set everything up from scratch again. The archive is roughly 600GB by itself so far, growing every day, and the backups are another roughly 3-400GB. My collection of movies and other assorted videos -- mostly youtube downloads hedging against them being removed -- comes out to 800GB, and my music currently tops out at 105GB but grows with each album I buy, physical or digital.
I find these numbers hilarious considering less than 10 years ago I was completely living out of a single 250GB drive and thought I'd never need more. Nevermind the fact that the collections of most others here dwarf mine by orders of magnitude.