Myself, for starters I believe that streaming services like Netflix are driving down the price of DVDs. In a world where the Internet is strictly forbidden, these movies will skyrocket, so I tend to drop in on the cheap $5 and $3.74 bins and pick up a movie even if I just have a passing interest in it. As of right now I have roughly 500 movies between BluRay and digital, though I do need to build up my TV watching for binge watching in my post-Netflix world’s bunker.
As far as books go, I've been frequenting Project Gutenberg and downloading books in the EPub format. I don't really know a lot about digital book formats and which ones are the best, but this seemed like the most open source version of an E-reader that wasn't just a plain text or HTML file. Right now I've downloaded almost 1500 books, from selected authors to randos I found with the search engine and main page features; I estimate that my library has roughly 9,800 books on its second floor, which houses all of the books besides large print and children's, so that's kinda been the goal I've set.
Gaming-wise, I've got around 2,600 games between ZZT and MegaZeux, and I've started downloading old DOS games too.
As far as hardware goes, I'm a bit more sketchy in this area. DVD players are easy enough to come by, and assuming they last for 10 years each I could probably easily hoarde away enough that if one breaks down I'd still have enough to last me a lifetime. I know the Raspberry Pi has its own form of DOSBox, and I don't know how functional Windows would be without the internet. I'm sure any Linux users are more than happy to lend their opinions here…
I suppose if all else fails you could go outside and actually talk to people, but I hear they have cooties.