If you had to choose the most ubiquitous bottled cream soda/root beer in NYC, Stewart's would definitely be at the top of the list. Found in almost all delis and many lunch joints across the boroughs, Stewart's is New York's craft soda of choice. Depending on which neighborhood you live in, you might also find Stewart's Key Lime or Orange 'n Cream or even Birch, Peach, or Grape, but I most often find the straight-up root beer, cream soda, and diet varieties.
I know there are many more varieties of bottle cap than my meager collection, but here we go:
Stewart's keeps it simple: I actually like the newer crowns better since they leave off the ingredients and let the logo really shine. It will never be in the HOF (sorry Stewart's!) but it's just the kind of root beer you'd want to snag at a moment's notice, which is another reason why I love living in NYC!