One of the biggest culprits of carbon emissions during the holiday season is all of the long car rides to get to Grandma's house. If you must drive, consider finding someone to carpool with who is heading in the same direction, to cut your emissions in half. Carpoolworld.com lets you register where you're going and helps you find others who are going the same route. While the eco-savings are huge, you also split the costs of fuel and tolls. The website has calculated they've taken over 173,000 cars off the road and saved 99 million gallons of gas.