I'm in NYC at least 5 times a month, but I always have 20k or more worth of camera gear in tow, so I can almost never stop to eat. I just love driving through the city, really hungry, smelling all of the great food. Occasionally, all I'll need for work is a camera bag's worth of gear, then I'll hit Katz's of just get a slice. All of the pizza places are now run by Hispanics, BTW, and the 'zza just keeps getting better.
Occasionally, I'll stay with a friend on the Upper West Side, and we'll hit the nearby
Metropolitan Diner (very good). When I'm working in The Bronx, I get lunch at a little
Mexican diner off the Grand Concourse at 149th. It helps to either speak Spanish, or to go there with a regular who does.
The only other places that I've eaten are a great little Polish restaurant on 2nd between 12th and 13th,
Little Poland, and the vending machines at the new Borough of Manhattan Community College building next to Ground Zero. The bottled water is always cold, but not too cold, and the Reeses are as fresh as you get straight from the plant in Hershey, PA. Avoid the Pop Tarts, though, they are dispensed from the fourth row of the machine, and often suffer breakage.