What's the best thing you've found inside a wall?

Or in a floor, etc. I'm putting up a new wall after a bathroom remodel, and the last piece of drywall is going on today.

I have a 2' section of 2" PVC that I want to stuff full of some cool stuff for someone to find one day. I'm gonna seal up the ends with end caps so moisture/etc won't get inside.

I've already got:

-A note from my wife and I.
-Photos of us
-A USB drive with a bunch of stuff on it (music, photos, etc)
-A small bottle of scotch
-A nice, triple-sealed joint (sealed with water, not saliva :)

What is the coolest thing you've found? What would you like to find?