This thread needs to be perked up......I know there are plenty of cheap mods left out there. Here are two more......
A rear seat cover for temporary or permanent use. One side is soft polyester fleece as shown. The other is a water-proof material......this one is gray/black, with a black back-side. The size is perfect...50"x60"......and is held firmly by my hatch cover. It's sold as a picnic blanket....Ace Hardware $12.
And here's a nice-sized small trash bag, that hangs on the headrest. Found this one (in gray/black only) at Office Depot. Case Logic.....$12.