Hmm. I can't say with absolute certainty what it the very oldest thing is, but I know I still have the disks and manual for Sim City 2000, from round about 1992.
Also, Transport tycoon, Wing Commander 3, Theme Park - All games from about the same period - 92 to 95...
And um, the Kings Quest collection, which I got in 1997, but does of course contain Kings Quest 1, going all the way back to 1984.
Oh, and I have an original cartridge for tetris on the Game Boy, which is second-hand, but otherwise must've been around since 1989...
I used to own more stuff like that, but several things have been stolen over the years.
And I sold my Atari um... I can never quite remember what it was exactly, but it was competing with the Commodore 64.
Anyway... My collection doesn't contain anything really ancient, but there's some pretty old stuff in there.