Thanks Ikea, for selling these good things. I have been using them to sort socks and underwear in my girl's closets, and whipped them out to keep the toys off the floor on our road trip. I have made a few modifications to adjust them to my needs. Mainly just tacking up the bottom and tacking the center of the top pockets to divide them into 2.
To use them best in the car I added loops of stretch elastic on the bottoms to loop around the grocery bag hooks on the backs of our front seats. It held them stable a bit. If you don't have those, you could attach ribbon and just tie it around. Whatever works in your vehicle. I even considered hanging these as window shades as well, but opted for these instead.