Pickup trucks - a major cause of roadside trash?

Ok this is probably going to make some truck owners mad, but its the truth as I see it.

The other day I was driving on 99 south and watched several white plastic grocery bags whoosh out of the bed of the pickup truck in front of me. I watched them float to the side of the road, and my eye immediately saw more debris. In a half mile stretch I saw the following trash items along the roadside: