A few days ago I was at my local supermarket and the checkout lady said, “Sir, please don’t double-bag your groceries.” Confused, I looked around and saw that my lane was the only one fitted with plastic bags. Apparently the store had run out of bags. How a huge supermarket chain could run out of bags was a little baffling, but it got me thinking about New York City Mayor Michael Bloomberg, who has proposed charging shoppers six cents per plastic bag, hoping to increase revenue for the city during hard economic times (one cent would go to the store, the rest going to the city) and contribute to his plan to make the Big Apple one of the greenest cities in the nation. Countries all over Europe have already implemented similar policies, with plastic bag use declining dramatically, and other U.S. cities have toyed with the idea as well. Many supermarkets, including mine, already offer incentives to customers for bringing reusable bags to carry their groceries. And selling those reusable bags could mean even more profit for stores. It remains to be seen whether offering incentives for bringing your own bag or charging a plastic-bag tax will be most effective, but our money’s on the latter. After all, consumers hate hidden fees.