Been, done it, husband has the New York marathon t-shirt!! I managed to hold the plane up both ways but am still not convinced that being shut in a tin at 30,000ft is a sensible way of travelling, in spite of the seat-back screen which allows you to choose your own films, music, games, flight maps etc. The security was thorough, although not the same at both ends. The little plastic bag for toiletries held enough daily lenses for a week, and on the way back I added 2 energy bars from the marathon goody bag just in case, and they were let through with no problems. We had no regrets about taking just carry-on luggage. Even US Immigration in Newark was ok - pleasant and even friendly.
New York is a great place and as soon as someone comes up with an eco-friendly way of getting there (floo powder?) I would go back!
Thank you all for your help, encouragement and good ideas.