I just finished the grocery shopping for a four day getaway with the guy I knit for. Despite a cart full of goodies, no plastic bags used. I'm not a super-hippie tree-hugger, but for a dollar's worth of cotton yarn and a few hours of tv watching/knitting, it's kind of nice to be rid of a few plastic bags.
I have two types, those knit with one strand of yarn and those with two. The two strander is more durable and can hold jars and jugs and such. I followed the everlasting bagstopper pattern from knitty, with a few modifications. No drawstring, knit handles reinforced with canvas.
The one strand bags are super stretchy (and I often regret putting such long handles on them) and are similar to this string bag, but not quite the same. I also really like the Saturday Market Bag by Jodie Danenberg and might try it also (free on ravelry). This one from the now deceased MagKnits looks really neat, too. I like the one handle look (the pattern is up on ravelry for free.)
Yay for grocery bags. Bonus if you love mindless knitting by the tv.