I would spend way too much time using this to pretend I had retractable claws instead of using it to carry things.
~Not-"Not-So-Handy Andy" Jack
Actually I think it'd be best to store your groceries UNDER the seat.
The Sack Saver is a mobile food-preservation angular momentum compensator.
Basically, it means that all your crap won't go flying around the car. You're welcome.