My husband and I are a huge fan of reusable grocery bags - we have been using them since 2004. We traveled to New Zealand and saw them in grocery stores there for about $1 each (unlike the US where only the canvas bags were starting to gain popularity for about $5-$8 each, if you could even get them in the grocery stores). We brought 6 home with us and have used them ever since. These are the bags that we bought in NZ (photo: wikipedia):
Besides green bags, there are a lot of other, really cool (even fashionable) options in reusable bags (some even made from recycled materials)! I just saw this awesome bag posted at design*sponge -- by artist Hayley Waring.
A lot of supermarkets in our area (NYC metro area) are now carrying all kinds of bags for about $1 - can't beat it! Great for groceries or whatever (I used them to carry my work to lunch, my laptop, recycling, beach towels, etc.) - you even get money back at some grocery stores (not that that 2 cents per is doing a lot for my grocery bill, but its the point that matters :)