This is interesting, because I was actively looking for a forum or specific topic on urban survival. Seems like almost all sites focus more on wilderness survival, where the plan seems to be go into the wilderness with a gun and a knife and live off the land until things get better. I don't know about anyone else, but I'm much more comfortable in the city, even after a disaster. I guess it depends on the type of disaster though, but except for maybe a Katrina type event (which are rare over here) or nuclear attack, I can't imagine an disaster big enough that would cause me to leave everything behind to go live off in the woods. Even after an earthquake, fire, tornado, etc, there are still more resources for food, shelter, and even water, in a destroyed city than in the woods. I assume most city people, even someone who's familiar with the outdoors, would probably be more comfortable in familiar surroundings in the aftermath of a natural disaster, than in an unknown wilderness.
One thing I've been doing is shifting my stuff for more of an urban environment. For one, I live right in the middle of the city, so it would be a lot more trouble to try and escape to the wilderness. Even after a large earthquake, there is still more salvagable resources here than in the mountains around me. A lot of the equipment is the same (knife, first aid kit, water), but I would probably reconsider bringing certain things like maybe a tarp or other wilderness specific items. I might also add other things like a prybar, emergency tools (for a vehicle), or firearm.