Living in Chicago, the most likely "not terribly disastrous" disaster would be some sort of power outage, possibly leaving me stranded on public transportation (has happened to folks here). My Streamlight Microstream is handy but not bright enough outside of total darkness (when you would most likely need a light anyway), but I've been carrying my 2-123CR Fenix instead. Much stronger light, probably a better defensive weapon than a folding knife (shine attacker in eyes and kick him when he's down, crank him in the head with it, blah blah blah), and it comes in handy at work. That and a SAK leaves me pretty well prepared for day to day stuff. When I have a backpack I carry a first aid kit, duct tape, extra batteries, big fixed blade,...
The most likely actual disaster would probably be riots. Stay low, be quiet, and get home. I know the city well enough that I'd be able to move discretely from anywhere I'd be. No firearms (Chicago laws are odd, should get something anyway) there, but we've a 3rd story apartment and solid doors top and bottom. If something horrible happened I'd probably be called up and handed an M16 anyway. Getting up to my unit in the suburbs without a car might be a bit more difficult though. :d