F1 and customs
I worked from the mid 1980's to early '90's for most of the Formula 1 racing teams supplying timing systems, speed traps, the first in-car telemetry, etc. and travelled extensively over Europe (usually in the middle of the night).
The company car was a long-bore Granada and used to attract a little attention, especially to bored customs officials in the middle of the night. Opening the boot for them to find boxes of strange, and expensive looking equipment used to light up their faces. I would just show them the Pit Pass for the F1 test I was going to, to immediately divert their attention and get me a hasty wave through. (Obviously I showed a Ligier pass on the way into France and a Ferarri pass on the way into Italy.)
I did have the carnet and other paperwork, but I can't remember ever having to show it in Europe.