I was going to suggest something pretty much like bearisgray suggested for the padded seat. I usually have a thick chair cushion in the car for events where the seat/bench is hard and could see simply using it with the saddlebag suggestion over the top. If it has the cushion inserted, it wouldn't fold up as nicely as having the saddlebag separate. As to the back--I don't know if they are still available or if they would work on a folding chair but several years ago Dollar Tree had a mesh device that works quite nicely on my sewing chair at home. It pretty much is the contour of a person's back but gives enough support to keep from tiring so quickly.