Is there any possibility you could bring your son, too? Is there anyone you can bring with you to New York to help you handle all three kids? If so, I think it might be worth it to bring him. Some babies who are exclusively breastfeed can have a hard time learning to drink from a bottle. Of course every baby is different, so if it's important to you to go with just your daughters, you'll have to do some preparation before leaving.
First of all, you'll want to spend some time for at least a week before you leave getting your son to the point where he will take a bottle. You might want to have someone other than you work on this. In addition, you'll need to pump enough breastmilk to leave behind. If not, he'll have to drink formula. And finally, while you are away, you'll need to pump at the same times that he would be eating back home. This will enable you to maintain your milk supply, and also ensure that your breasts don't become engorged.
And if you do bring him to New York City for the day, don't worry about where you'll be able to feed him. It's quite common to see women in NY breastfeeding their babes all over the place. You'll have lots of company.
Guest breastfeeding expert Andi Silverman is the author of Mama Knows Breast: A Beginners Guide to Breastfeeding and a mother of two. Read her blog at www.mamaknowsbreast.com, and send your questions to firstname.lastname@example.org