I worked in downtown Baltimore for 12 years, and got put in some interesting scenarios in that time. I agree that most disasters in an urban setting equate to "How do I get home?" because very few workplaces are well-positioned to be a place of refuge for any length of time.
I have always EDC'd a multitool, small flashlight, and a lighter. Other items have come and gone, but these have always been the core. In the past few years I have increased this to include an EDC backpack that is ostensibly for my laptop and its accessories but also contains:
- radio/flashlight that charges by solar/crank/USB cable
- water and food
- protective gear including dust mask and ear plugs
- Esbit stove and metal cup
- PSK including DR PSP, AMK first aid kit, poncho, Heatsheets blanket, small folding knife, small Leatherman tool, lighter, bandana, etc.
- USB key with encrypted vital docs

Wilderness survival is about surviving until you are found. In an urban setting you are probably never going to be "lost" in that sense, so the goal is safely getting to a place where there is security, shelter, and sustenance; this gear is meant to do that.

All this lives in a smaller bag about the size of a thick hardcover book that will easily pop out of the larger backpack. Ideally this would have been augmented by the larger Get Home Bag in the car trunk, if my car was accessible.

I also had maps for the trek home, if that became necessary. 40 miles would equate to several days even without any major problems, so the plan was to go light and fast.

None of the things that I experienced (Train tunnel fire, 9-11 general freak out, building fires, bomb threats) required walking home, but having some gear and having thought through some possible scenarios always made me feel like I had an edge in dealing with the things that came up.