Also remember to drink water if you exercise for more than an hour. Diluted sports drinks or weak juice are good recovery beverages after heavy exertion; you'll be fine with just water after a standard session.
You don't need any salty food during or after exercising. You'll get enough salt as part of your regular meals.
Walking is the best exercise to take after a heavy meal. If you want to exert yourself, wait a couple of hours to let your digestive tract empty. Exercise will be more fun then, too!