Erin, you must go to the Metropolitan Museum of Art - It's magnificent - also has a nice cafe
where you can hang out.
The Upper West Side is indeed a food mecca - I lived there for over 20 years, but haven't been back in 10 (Aiiieee - has it been that long???!) Zabar's and Citarella's were already mentioned - there's also Fairway, West Side Markets (used to have the best Parmigiano Reggiano), H&H Bagels...
Whole Foods is at W.59th and Broadway and there's also one at Union Square. There's also a Trader Joe's at Union Square, E.14 St. (neither was there when I was living there).
All my favorite restaurants have since closed, so I can't recommend any, but I'm sure you'll find lots!
Good luck with everything!