Dan,

I used to carry about as much as you, and the Blackout of 2003 taught me a thing or two about a realistic kit for NYC. I'm in NYC all the time I used to live there as well.

First of all, water. Water, water, water. Did I mention water? In an urban environment, your opportunties to scrounge, steal and buy stuff are far greater than in a rural or suburban area, but water is a must.
After that, light. LED lights are the way to go for battery life. The new Pelican recoil LED lights kick butt, are light and have huge battery life.
Next is communications. A cell phone, tiny radio and spare batteries are a must. After that, a leatherman tool. Get a Wave or something decent like that. Put a Fox 40 on your key chain, put a tiny LED keychain light on a necklass.

With just that kit, you're well on your way in NYC. If you have an NBC attack, you're going to be stripped naked, thrown into what amounts to a carwash for humans, and everything you were carrying will be carted off as hazardous waste and destroyed. And if you're in a car bomb situation, if you survive the inital blast, you're going to either be entrapped, wounded, helping or unaffected. None of these situations calls for heavy equipment. NYC has - without question - the finest emergency services in the nation. You're no more than 3 minutes from a full response from a massive team of well-trained people. Of all the cities I go to in the USA, while I feel that NYC has the biggest "bulls-eye" on it, it's also the city where I feel most confident in the ability of the government agencies to respond and act appropriately to a major incident, so I pack MUCH lighter than I would in a place like LA or DC, or Chicago.