So let's talk about the alternatives. Someone gave me an Envirosax and it's awesome - the fabric design is cool and I love the construction. When it's all rolled up and fastened with its snap, it's small enough to carry around all the time (4 x 1.5"), and then when it's unrolled it can carry loads of stuff. Just ask Justin Timberlake (who has the same style as me) or Kelly Slater (obviously someone you can trust because he's the world's best surfer).
I've also just obtained ZPM's gorgeous new invention called Bagz. (So far Justin and Kelly haven't been fortunate enough to receive theirs, but no doubt they'll be keen to do so when they learn this natty invention was highly commended in the recent Gift of the Year Awards.) Folded up, the Bagz is roughly three times the size of the Envirosax, but then it does contain three bags. Unzip the pouch to release two shopping bags, and you'll find that the pouch actually becomes a pocket on the outside of a third bag. A snaptastic strap lets you attach the whole shebang to the handle of your shopping cart. As with most ZPM things, the fabric is tasty and if it hung around for your entire life, you might not be too sad about it.