My Reply:
"First, we need to kill and eat the weakest of us.
Next, everyone pees into this pot, we'll distill drinking water.
I've got some scotch here in my drawer, go get some cups. "

No, OK, seriously. We're in New York City, and the scenario you're talking about is so unlikely as to be not really worth planning for.

HOWEVER, there is a scenario that is similar that IS worth planning for, and that's a "dirty bomb" in the area, which would force a shelter-in-place for a bit of time. I don't think it would kill utilities off, it really depends on where and how the detonation happened.

I've already been named as the "Emergency Management Coordinator" for the office, and we hold occasional staff meetings to discuss fire safety and emergency preparedness.

We're 64 people on this floor. At any given time we have about 100 gallons of drinking water on hand in the form of those 5 gallon water cooler jugs, and the building itself has a set of very large water tanks on it, so we're gravity-fed so the water supply would be available. There's a few things I'd do with water supply and sanitation (grab water and fill the empty water containers, and make sure that we held out enough water for flushing toilets if the big tanks ran dry).
The people I work with are smart and resourceful, and I'd think that we'd be quite adept at managing ourselves and our supplies. Food would be an issue, there's not much here, but if we had a confirmed dirty bomb incident and the streets were too "hot" to go outside until decontamination, I don't thing we'd have trouble keeping people on low rations for 72 hours.

So in short, while I'd expect to be called on for emergency management, I also have a lot of confidence in my office and company ownership to do what's right and prudent in an emergency.