Used just yesterday: a twelve-inch cork-backed metal ruler that I "borrowed" from my dad sometime in the early 1980's. Possibly late 70's since I've been a papercraftin' fool since I was a kid. Also used a couple days ago: a 30-60-90 triangle I "borrowed" from my mom around the same time. I have the matching 45-45-90 triangle and an 18-inch metal ruler I "borrowed" from them too. I was always using them so I guess they just let me keep them. I still have the X-acto knife I got in 1986 for an art class my sophomore year in high school. I think those are the oldest things I have, and I still use them all the time.
Fun topic, thanks!