Walk or take a bike to work whenever possible. Find out if your office is close enough from home to do this, then try it at least twice a week.
Find out how far it is to the bus or train station from your home and office (if these are available). You can use this trip for exercise by jogging or power walking to the bus or train.
Try tummy toning exercises while in the car. While sitting straight, breathe deeply into the abdomen, push the air up to your chest and exhale slowly. Another way is to inhale, lean forward and exhale while blowing out a little extra quickly.
Try isometrics and curls with the steering wheel. Grasp the wheel with both hands, push into it, lean forward and pull out. Or, hold the wheel at the base of the wheel and pull up toward you. These are best when stuck in traffic jams.
Park as far away from the office as possible. If you take the farthest parking space, the extra walk can be good exercise too. You also may have an easier exit at the end of the day as well.