I consider myself a realistic idealist, if that makes any sense. I have a few - but not too many (that's the realist part) - core principles to which I adhere with all my might, and I try to live them every single day.
One of those is living in a reasonably eco-friendly way. Being a New Yorker makes this a lot easier - haven't owned a car in eight years, don't buy bottled water (NYC's being the best tap water ever), live in a small space, use mass transit, donate old belongings to Housing Works, buy as much food locally as I possibly can, and so on.
One more thing I've started doing in the last 18 months or so is carrying re-usable shopping bags everywhere I go. I carry a combination of canvas tote bags (which fold up nice and small) and sturdy nylon shopping bags. The canvas bags are great for books, clothes, and greenmarketing (keeping your purchases slung over your shoulder makes it a lot easier to check out the next stand), and the nylon ones are perfect for toting your lunch or an all-in-one grocery run.
My favorite nylon bags are the ones by Baggu - there's just something stylin' about their shape, and they come in every color under the sun. When it comes to canvas, my favorite sources are the Etsy sellers The Craft Pantry (who made the bird tote and French produce sacks above) and Jose Pulido. (You can also find re-usable produce bags made of netting on Etsy.)
So go on, take the plunge - you'll look cool, and feel cooler. Seriously.
Photos courtesy of The Craft Pantry and The Monterey Garden Club.