Inflatable Seat Cushion
My wife had back surgery.  She needed something to soften up the ride in our rather stiffly suspended car - especially on the less than smooth freeways of today.  The problem with it is that the surface does not permit her to slip across easily to a proper sitting position.  Putting a piece of more "slippery" plastic over the top has made it usable for her.
Rating: 3 stars