Any suggestions on cool things to do outside of the obvious or mainstream options?

I'm wondering the same. We are going for New Years, but will have two extra days up there to fill. Just wondering what the "must sees" and "must eats" of NYC are.

Depends on how you define "mainstream." It's going to be cold and unpleasant to walk around for too long, but if you're around before Xmas, check out some of the xmas villages, especially around Columbus Circle and Bryant Park. Hit the museums: Met, AMNH, MOMA, Morgan Library, Guggenheim. I'll add to it as I think of stuff, but if you search for New York and Christmas, you'll see other threads of a similar bent.

911 museum just opened recently, most definitely worth it.

Got back last night. Mainly visiting friends but did a few of the holiday staples: Macy's, Saks, Rockefeller Tree and the Nutcracker on Sat. night. We gave up pretty quick w/ the crowds.

It's oyster season! Highly recommend Maison Premiere in Brooklyn.

Buddy we visited is the wine director at Marta. He's a CS native that's climbed the ranks of the NYC somm industry.