Only 7 days? [;)]
You could easily eat yourself broke in Manhattan in a week, or you could easily eat streetfood and never get tired of it.
Yep, gotta do at least one dirty water (Sabrett’s). I like the sausage with mustard and onion sauce, myself.
Since my favorite streetfood, Hallo Berlin, has already been mentioned, here’s my close second: http://www.roadfood.com/Reviews/Writeup.aspx?ReviewID=2224&RefID=2192
Be aware that some of the better street vendors in Midtown don’t set up on weekends. I don’t think Rolf Babiel (Hallo Berlin) does, but he is in the neighborhood of MoMA. Also be aware that many Jewish-owned establishments will be closed on Saturday (not a great day to go to the Lower East Side).
Lots of good places to get a gyro, most pizza places make a decent one, but I’m surprised at a recommendation of Gyro II. It’s been many years, so the place has probably changed, but they used to make their tzadziki with mayo instead of yogurt. Feh!
How ’bout a stroll up Broadway on the Upper West Side? Window shopping at Fairway and Zabar’s, maybe bagels from H&H? I especially enjoy people watching in the residential areas like this on workdays.