New York Cares is an organization that is basically a clearinghouse for other volunteer opportunities in New York City. I went to their orientation some time ago and now I can sign up for any volunteer opportunity on their website. Other organizations go to New York Cares and put up their needs and volunteers can register for whatever they want.
Every year, they have something called Winter Wishes (click on link above for more information). Basically, kids write in and say what they want for the holidays (probably Christmas, but you never know). What you do is sign up to take a letter that someone wrote and get whatever the kid wants. They don't expect you to spend more than $40 and you can get a different gift if the one requested is too expensive or hard to find. For some kids, this is the only gift they have.
Anyway, feel free to sign up. I did. (Oh, and tomorrow is the last day to sign up.)