One big thing you can do for the environment is to cut down on your consumption of beef, chicken, fish, lamb, and pork, or even go vegetarian (though that's very hard, I will admit). Even a small reduction in the amount of meat you eat each week can make a difference to the environment.
1. More than half our water in the USA goes to feed livestock.
2. Livestock consume more than 70% of the grains and cereals we produce in the USA.
3. Livestock (especially cattle) degrade landscape very quickly, land that could be reforested or replanted with native plants.
There are many more reasons: health reasons, emotional appeals, etc. As I said, going vegetarian isn't something I push on people because it's hard in many ways. Still, buying a little less meat at the grocery store is something you can feel good about, and something that will encourage you to eat more vegetables--which is always healthy.