Door pockets always have baseball caps in them so I don't burn my bald noggin and the wife's hair isn't too wind blown upon arrival. I also keep a microfiber towel in the driver's door.
Oddments tray has the damper key for the coil overs and an air gauge.
I've discovered that the amenity kit box/pouch Lufthansa gives you when flying business or first class make for a good "emergency stuff holder" for the Boxster. Spare fuses, small tools, pocket knife, spare set of gloves for working on the car in an emergency, etc.
I would keep the things after every flight, but it took the Boxster to find a use for them. Well, for one anyway. There are about 4 more sitting in the closet still.
Sounds handy, I could take one off of your hands if you need them gone.