Kurt and Rachel visit the set of Wicked, and sing a song from the show, sung by the characters Glinda and Elphaba the Wicked Witch. Kristen Chenowith (April Rhodes in Glee) was the original Glinda and Idina Menzel (Rachel's birth mother in Glee) was the original Elphaba.
In the beginning of the episode, the billboard for How To Succeed in a Business Without Really Trying can be seen. Darren Criss, who played Blaine Anderson, went on to star in said musical.
The music playing over the first scene, in which Rachel stands in Times Square thrilled to be in New York City, is from George Gershwin's 1924 composition "Rhapsody in Blue." Although Gershwin wrote a great deal of classic Broadway music, this piece is more often performed by symphony orchestras; its association with New York City and Broadway instead comes from its use in the opening montage of New York scenes in Woody Allen's movie Manhattan (1979).
When Will (Matthew Morrison) is singing on the broadway stage, he is singing the song "Still Got Tonight", an original off of Morrison's own self-titled 2011 album.
Prior to singing "My Cup," Brittany is seen tracing the circumference of a hotel-room water glass.