First, the easy answer - which is less harmful on the environment, flying or driving? Flying. Experts at National Geographic say that flying accounts for about 3 percent of the world's total greenhouse gas emissions. But if you're considering longer flights, such as those across the United States, driving is better. Such a flight would emit close to three tons of carbon dioxide per passenger, but driving could roughly double one's emissions. The train, however, is the best bet.

Now, the hard answer: paper or plastic? You probably hear it during almost every grocery-shopping trip. The answer: neither. Carry your own bag or crate.

Seven out of 10 Americans don't know that plastic comes from petroleum. Thus four out of five grocery bags in this country are plastic, using toxic chemicals and about 12 million barrels of oil, and resulting in the litter of about 4 billion plastic bags. Plastic bags are not at all biodegradable but can be recycled although it is time-consuming and expensive. Plus, many bags collected for recycling are actually shipped to countries like India and China where they are cheaply incinerated.

However, paper bags require about 14 million trees to be cut down every year and use toxic chemicals during production. While paper is degradable, typical landfills lack the water, light and oxygen to completely break them down. And recycling them requires returning the paper to pulp by using harsh chemicals, and recycling most likely turns them into corrugated cardboard, not new paper bags.