Consumer goods ~
Just as we often forget the impacts of the "new" formaldehyde smell associated with furniture on our health, items such as clothing and furniture can have a large impact on your carbon footprint. Buy durable items that you will have to replace less often, and can be donated if you decide to change your look or home décor.
Think about how many miles a week you drive in your car and what its gas mileage is. Consider how often you utilize public transit systems. Then think about many hours you spend being told to fasten your seatbelt on a plane each year. Public transportation is generally a more efficient choice than driving. Take the metro, walk, or bike. It is good exercise, and may save you time, considering DC traffic. Avoid the parking hassle too.
Flying is also a very energy inefficient way to travel. Road trip instead, or plan a "staycation" and relax at a nearby hotel instead of taking a trip to Hawaii.
Food and Water~
Buy local! There are some excellent farmer's markets in the area. Not only is a farmer's market adventure a fun outing, but generally the food sold is tastier and promotes sustainable habits. that can make for delicious food, sustainable habits, and a nice weekend activity. Buying local often not only means healthier food, but energy is saved on the shorter distance the food has to travel.
Certain foods require a lot of water to grow. For instance, a 1/3 lb burger typically takes 660 gallons of water to produce. Did you know it takes significantly less water to produce a grape than to produce a walnut? In your home, install low flow shower heads. Once again, this will reduce your water bill as well. Win, win.