Chelsea Market is shit. I have no idea why people like it.
Eataly mostly the same. Walk in, look at the throngs, walk out.
The Flea Market is in Brooklyn, so why would you go there?
All the museums are good, but the big ones are exhausting. If you want NYC specific, The Tenement Museum and The Museum of the City of New York are small and interesting.
NYC is a walking city. Pick a direction and walk. Eat when you're hungry at some neighbourhood restaurant. You'll...