After 9/11, a lot of people who work in DC began keeping sneakers at work (many probably buried in credenzas now). Some of us added a backpack with essentials such as a flashlight. I would advise those who could face a longer hike to keep a small backpack in their office that contains supplies appropriate to the season, including:

sneakers + socks
waterproof parka + hat
map (may take a different route walking than when driving)
cash
waterbottle(s)
flashlight/headlamp + batteries
small radio (you'll hunger for news)
pen and paper (small moleskin is great)
eyeglasses, if needed
energy bar
First Aid
cotton bandannas (many uses)
knife-Leatherman
pepper spray


Obviously in winter this should include warm gloves, hat, etc. In summer I'd want powdered Gatorade in there.