The Great Gatsby is a realistic novel in its historical setting of the 1920s, a time that Fitzgerald himself named the Jazz Age. In its portrayal of the flapper, represented by Jordan Baker, the cars of the era and the fascination with them as well as the reckless behavior that accompanied their invention there is, indeed, much realism. The songs that play in the background such as "Beale Street Blues" and "Three O'Clock in the Morning" are from the era.
Certainly the people from East Egg are caricatures of the people with whom Zelda and F. Scott Fitzgerald associated when they lived in the East; Tom as the supercilious and overbearing man of money and position is representative of some of the men with whom Fitzgerald was acquainted.
His speaking voice, a gruff husky tenor, added to the impression of fractiouosness he conveyed. There was a touch of paternal contempt in it, even toward people he liked--and there were men at New Haven who had hated his guts.
Described as a lyrical realist, Fitzgerald conjures images and evokes emotions with his descriptive and poignant scenes that realistically portray people's desires for material acquisition.
The setting of the novel is a real place. East and West Egg were sections of New York that actually exist(ed). The difference in societal strata was determined by how wealth was attained, whether it was "old money" (inheritances passed on from generation to generation) or "new money" (money that had been earned through an individual's hard work and entrepreneurial skills). This also determined where one lived. The new wealth lived in West Egg and the old wealth in East Egg. Such class distinctions are common even today.
There is a distinctiveness about each of the classes - new wealth comes across as rough and ready while old wealth is distinguished by a hierarchy and sophistication, as it were, lacking in new wealth. These distinctions are obvious in the novel. Tom Buchanan's haughtiness is derived from his being of "old money." He looks down on Jay Gatsby who is "new money." "Old money" provides security and stability, whereas new money could be lost just as quickly as it had been gained. That is part of the reason Daisy decides to stick with Tom and not leave with Jay.
Furthermore, the novel is set in a period immediately after the end of the First World War. After the misery, pain and suffering endured during "The Great War," it was a time for celebration. People were expressing the freedoms they lacked during the war. Over-the-top, indulgent parties were the order of the day, as illustrated by Jay Gatsby hosting extraordinarily flamboyant parties and Tom's continuous little excursions to his apartment in New York to have fun. Everybody during this era was out to have a good time.
The characters are realistic. Jay Gatsby symbolizes those who, during this era, sought to fulfill the "American Dream" - a dream of wealth and success beyond one's wildest dreams - attained through hard work and success. Even Nick Carraway searches, to a lesser degree, for this ideal of success by moving to New York. Myrtle Wilson and her husband George seek better lives. The dream is still alive even today. Many foreigners leave their countries and come to the United States of America in search of this ideal.
The affair that Tom has with Myrtle Wilson is as realistic today as it was during the "Jazz Age" in the novel. People with power and wealth have always indulged themselves and their fantasies just so much more than "ordinary" mortals would, and they would mostly get away with it - just as Tom did.
The plot is realistic. The unfolding tragedy deals with real situations and is not just a contrivance of the author's imagination. When things can go wrong, they will, as happens with Jay, Myrtle and George Wilson. Ordinary people become ensnared in extraordinary situations and circumstances, in many instances contrivances created by those with money and power - as in the novel - and become victims.
These are a few examples of realism in The Great Gatsby. All in all, the success of F.Scott Fitzgerald's brilliant novel lies in the fact that he presents us, the readers, with realistic scenarios that we can recognize and identify with, no matter what our status.