First Flight Covers
I was never a serious stamp collector (I think philatelist is too fancy a term), but I did collect some first flight covers while I was employed at the airplane company that used to be located in Renton, Washington.
I witnessed several first airplane flights, but the one that had the most significance for me was the 747. When I started working on that program the airplane design was still being refined. I saw the first takeoff three years later, and quite a few more during the flight test program. I also flew as an observer during some of the test flights. It was a very exciting time and I'll never forget it.