1.If possible, take the train. It consumes less energy and produces less pollution per passenger-mile than driving, boating, cruising or flying. And it's an interesting way to travel. Plus it allows you to get things done, if you have to, during the voyage.
2.If you stay in a hotel, minimize your footprint. Reuse your towels, minimize use of your room heater/air conditioner, and don't waste water. Better yet, stay with a local -- you'll learn more, conserve more, and save more, and probably have more fun.
3.Use recyclables and reusables. Take your own travel mug. Avoid disposable dishes. Don't contribute unnecessarily to garbage, and recycle whenever possible.
4.Buy local, natural, organic, vegan foods. And buy other local goods instead of imports, including crafts and souvenirs.
5.If you're on vacation consider cycling, sailing, hiking, cross-country skiing, walking tours or eco-vacations instead of combustion-engine powered trips. At your destination, take a coach or public transit (if it's safe) instead of a car or taxi.
6.Turn stuff off at home. Don't waste a lot of heat or electricity if there's no one there.
7.If you have to drive, use cruise control, don't speed, make sure your tires are properly inflated, and ensure that your car's tuned up. Dress appropriately rather than using car air conditioning or heat unnecessarily.
8.If you have to take your computer, use it sparingly and turn it off when not in use.
9.If you're visiting businesses, help them save energy, money and the environment by conserving resources, especially by turning off or down heat, air conditioning and electricity at night and when otherwise not in use.
10.Buy stuff that lasts. Avoid disposables, cheap clothing, poorly-made souvenirs, overpackaged goods, non-rechargeable batteries, and stuff in non-recyclable containers.
::The Environmentalist's Travel Guide