I have a total of ten -- all from one of the local grocery chains -- unless there is someone else in the car with me, I keep them right on the front passenger seat. After I empty them in the house, I set them right beside my purse so they get back into the car the very next time I do.
I really think they are a great thing . . . but there is one drawback . . . since I'm not collecting plastic bags anymore, I've had to buy special bags for my garbage and my kitty litter.