As you wrap up your weekly grocery shopping and get in line at the supermarket, it's time for yet another difficult choice. The cashier mechanically spouts at you, "Paper or plastic?" referring to what kind of bag you'd prefer. For some people, it's a stressful decision. Convenience is pulling you toward plastic, but a nagging green conscience might automatically pull you toward paper. However, it's raining, and if your paper bags break, it could ruin your purchases. On the other hand, is it selfish to put immediate convenience over the thousands of years it might take for a plastic bag to degrade in a landfill? But, what a minute -- aren't we encouraged to save the trees and avoid overusing paper?