Here's an embarassing one: I recently worked on the A/C in my wife's '98 Lumina. In the course of the repair I ended up having to remove the air cleaner box to get access to the low-side port; and I also removed the caps on both a/c ports.
Anyway, when I moved the car, this part was laying on the driveway:
I just wanna make sure it's not something important. Any help will be much appreciated! JohnB