I've already have my top list:
-Central Park Picnic with some goodies from Dean & DeLuca , discover all the hidden places!

-Visit the museums I've missed the first time! the Met, Guggenheim !

-Take a break and read a nice book at the New York Library Main Branch,

-Have some yummy cupcakes!! This ones below were from the famous Magnolia Bakery,

-For lunch adventure myself in China Town!!

-Climb to the top of the Empire State Building! The picture below was taken from the top of the Rockefeller center

-Get discount tickets for a Broadway musical!

-Go for the first time to a opera production at The Metropolitan Opera
And definitely get lost wondering Manhattan's coolest neighborhoods. Any advices are more then welcome! :)