For me music is the most important thing about American culture.

Almost all of our music is a mix of traditional white and black music- gospel, the blues, jazz, rock and roll, country, and rap all started in the US. Think about all the music worldwide influenced by those genres. There's also Broadway in New York, and Hollywood. Hollywood isn't always bad, look at the original Star Wars or Citizen Kane.

As for writing, Ernest Hemmingway and F. Scott Fitzgerald are as popular and as influential of writers as Twain, and Herman Melville and Emerson, Throeau, William Llyod Garrison, and Walt Whitman are less famous but still very skilled and important early American writers. Mark Twain's books are still funny and incredibly well written, but at the time he was infamous for using contemporary spoken language instead of the 'correct' written language.

There's the "car culture" where everyone is expected to have their own car and drive it to work each day (this is dying out).