Stop into the Tiffany flagship store (57th & 5th) and browse. Several floors of sparkly goodness.
If you're into Indian food, check out Devi (8 E 18th St., just off 5th) and/or Sapphire (Broadway between 60th and 61st, not far from Lincoln Center). And you haven't lived until you've had a pretzel from a hot dog vendor. Unfortunately, most of the restaurants I know of in Manhattan are on the pricey side, but I can always get my parents to foot the bill.
Plays - I don't even know what's playing these days.
Have fun!