Answer "Neither" when the bagger at the checkout asks, "Paper or plastic?"
If you haven't already made the switch to cloth, hemp, or durable plastic, give it a try today.
Any company who has a product to advertise wants you to carry a bag with their product's name on it and this month, so there are a few free bag offers I stumbled upon in just a quick google search.
Here are two offers for FREE bags, with minimal effort -- and no purchase -- involved:
Sign an Earth Day Pledge
Submit a Design
Or, if you dislike advertising as much as I do, you might want a blank canvas for your own message or no message at all. My cheapskate tendencies take over when the product is free, so don't pass up the above offers. But if you're like me, you need more than two bags at the grocery store. If you'd like to design your own logo for your bags, visit your favorite local or online craft store, or maybe even at an office supply store, buy a pack of iron-on transfers for about $5 for 5 transfers. Set up your design on your computer and print directly onto the transfer. If your logo involves words, you'll have to print it as a mirror image onto the transfer or, on my Mac, there is a "transfer" option in the print menu that reverses the image.
I used iron-on transfers on several bags from ECOBAGS, which is giving away a free string bag with the message "Earth Day is Every Day" to the first 250 purchases of $50 or more. $50 is going to get you a lot of bags on this site, which has bags made of organic fibers by companies with fair labor practices.
If you make your own, please share with me a photo of your handiwork!