What is your car's rarest option?

I got to thinking about what item I would love to find for my car (1966 Barracuda) that I just couldn't find. I soon realized that most of those items I was able to find if I looked long enough and had enough money to buy it. One item that I still haven't found or even seen a photo of is the optional factory mattress for the rear compartment. Anyone ever seen one or have a photo of one? How about your car? Is there something that was available that you have never seen?