In New York, a few restaurants still require men to wear jackets and ties. In general, New Yorkers tend to dress a bit more formally than their Midwest or West Coast counterparts for special events. Jeans and sneakers are acceptable for casual dining and sightseeing just about anywhere in the city. Always bring sneakers or other flat-heeled walking shoes for pounding the New York pavement.
In spring and fall, pack at least one warm jacket and sweater, since moderate daytime temperatures can drop after nightfall. Bring shorts for summer, which can be quite humid. You need a warm coat, hat, scarf, and gloves in winter; boots for often slushy streets are also a good idea.