Source codes. I'd love to see a lot of games source codes. Games like League of Legends, I'd love to see just how bad it was coded; there's supposedly a lot of spaghetti code and "bandaids" that I'd love to see what the programmers at Riot have to deal with on a daily basis. Then there's stuff like No Man's Sky that supposedly uses a lot of actual science and evolution methodology to create the planets and life on those planets. Those algorithms would be really interesting to study.
Top secret government information, who knows what's in there.
Cable news memos explaining how they're going to spin the news. I think it would really help us quit fighting each other and get some serious work completed at the federal government level.
This is interesting. To add, correspondence between various politicians and their staff. See how much the spin doctors work.
All the things on the Sims franchise 3 and on.
Source code so that modders can build a game more receptive to mods and serials codes and whatever.
I'm sick of buying serial codes so I can make a swank house.
Who/what sank the bugaled breizh