This whole extra is all in the theme of glorifying Gatsby's parties. The narrator (Nick) start by describing the party, from how guests are transported to the party, with the Rols-Royce, with a station-wagon or by boat. Only by this, we can already see that this party is truly extraordinary. Nick goes on to describe other aspects of the party that differ from ordinary back-yard parties. He states that instead of bought orange juice, Gatsby has himself brought racks of oranges from the fruiter, and has a machine, operated by butler, whose only job is to press a button, in order to produce the orange juice. He also mentions that Gatsby invited an entire orchestra to play music, professional dancers, and showgirls just so there's always what to look at.

From the size and type of the party, (and we know that he "throws" these parties every Saturday...