Tetris (PC, C64, Tandy, Apple) - I'm a huge Tetris junkie, no doubt about it. So when I saw an original 80's computer version of this CIB, you can imagine my surprise and joy at finding this. It had both the 5.25 and 3.5" disks and everything. It was also compatible with just about every major system available at the time, a trend only coming back to PC gaming after 20 years of Windows majority.
Holy cats! I actually have this floppy. I really wish I could play it, but I need the manual with the passcode to play it. It sounds lame but software piracy (and computer viruses) were present before most computers were connected to the internet. People just copied things on floppies instead of hitting up the latest torrents. Anyways I picked up a monster stack of 5.25 floppies from a garage sale for like $2 a couple years ago. Most of it was copied stuff, but a few originals were there that are still worth playing like Arkanoid and Bubble Bobble.
Another note, for the end of the cold war era, the multinational publishing and outstanding success of Tetris was profound for the time.