Slip them on for walks at lunch and on breaks. Buy a backpack. Instead of driving to all your errands, walk as much as possible, and use your backpack for purchases. Instead of meeting friends for lunch, coffee, or dessert, make dates to take walks, go dancing, or go for bike rides. Or make a date to visit a health club.
Most clubs allow free one-time visits to check out the facility.
Walk your dog. If you don't have one, consider getting one. Dogs are great exercise companions. Make breaks count. During breaks at work or television commercials, get up and stretch or walk around.