On days when it's nice out and I have places I need to go around the city, I wear comfortable shoes (or workout shoes) and throw some extra clothes in my backpack so that I have the OPTION to exercise -- meaning, if I decide I want to take a brisk walk between places I need to be, or after a meeting or rehearsal ends, I can! I can just do it, then and there, with no other planning. And if I've packed that stuff...I almost always end up saying YES to the option!
Just don't make your backpack or carrybag too heavy, since you'll be wearing it on your walk. :)