Take a look at the dangers wild animals face from plastic bags...
Among them: Nearly 200 different species of sea life, including whales, dolphins, turtles, and seals, plus thousands of birds, die every year because they mistake discarded bags for food or get so entangled in the bags they can't survive.
You can get a reusable shopping bag at your grocery store for only $.99 or $1.99 at most. Buy six of them for less than ten bucks and do the animals a favor.
More good info on plastics: