I left a digital camera on an FR plane at STN in 2000, it was under the seat and well out of view. I remembered within seconds of getting off and tried to go back but security were not having a bar of it and insisted I went to lost and found in the baggage hall.

Well guess what... When they called the FR gate and the agent went to look under the seat number I gave them there was nothing there... And I was pretty much the last off the plane. Draw your own conclusion.