Well they just put up the tree at rock center, although it isnt decorated yet, you could go ice skating at rock center, that would be fun. Statue of Liberty? Empire State? have you already done these things? if not you should do them. Or do a pub crawl down second ave. thats always fun, even on a wednesday afternoon
I would walk the Brooklyn Bridge. You get some really fantastic views of the NYC skyline. And once you're in Brooklyn, stop by Grimaldis for some pizza. It's not far from the bridge.
That's a tough question... I mean, to want to re-do something would imply that there is something that you regret having done in the first place. Part of me wants to say that there is nothing I would re-do because everything that has happened to me up to this point has made me who I am... and I am generally happy with that.