Take Earthbound Farm's Conservation Quiz, score at least 9 out of 10 and they'll send you a free shopping tote! The questions are fairly easy if you have some knowledge about environmental issues, and if you get stuck there are links to articles with the answers.
Here's the fine print from the website:
Offer good for US and Canadian residents only, while supplies last. Quiz must be completed before Midnight PDT, April 30, 2008. One bag per mailing address. Bags will be shipped to recipients in June, 2008
More and more grocery stores are offering discounts if you bring your own bags (Festival gives me a nickel a bag!), so this is a gift that keeps on giving!