In The Great Gatsby, F. Scott Fitzgerald writes that “life starts all over again when it gets crisp in the fall”—and that is certainly true in New York City. From the Upper East Side to the West Village, emerging trends and ideas can be caught between laments of skyscraper-high rents and the clinking of martini glasses at the bars of glamorous hotels and local dives. Over brunches and sidewalk run-ins, tales of summer sojourns out east and overseas are retired for tips on the top tables and show...