There is one main scene here that serves both to plant this novel (again) in the heart of the reckless 1920s "roaring" culture as well as serve as a grand element of foreshadowing.
Let's describe the scene first and look at it in historical context. Put quite simply, this scene involves a drunk driver. One of the guests at Gatsby's party who had too much to drink got behind the wheel of a car and tried to drive it. Not even off of Gatsby's property yet, the guy crashes into a wall and lands the car in a ditch, the wheel flying clear off.
The "puzzled" passenger is Owl Eyes (another minor character in the book) and an unnamed driver. Owl Eyes kind of gets out of the car and scratches his head. Only after making a few stupid comments does he admit that someone else was driving the car. You see, a crowd had gathered. They came to gawk at yet another one of Gatsby's party debacles.
Everyone watches amused (and saying "Ah-h-h") while the drunken man gets out of the car and says, "Wha's matter? ... Did we run outa gas?"
Seriously? The roaring twenties at their best.
Now, the significance of this scene can be defined by one word: foreshadowing. There are two passages in particular that are notable in this arena. The first is, in itself, a description of the scene and more specifically of the gawking crowd that surrounds the crash site:
As they left their cars blocking the road, a harsh, discordant din from those in the rear had been audible for some time, and added to the already violent confusion of the scene.
This first bit of foreshadowing is a general kind that shows these lavish parties and drunken debauchery can end in nothing good. Nothing specific about Gatsby here, of course, but after a "fun" night of dance and drink, ... it was important for Fitzgerald to show us that all of this "roaring" has consequences.
The caterwauling horns had reached a crescendo, ... A sudden emptiness seemed to flow now from the windows and the great doors, endowing with complete isolation the figure of the host, who stood on the porch, his hand up in a formal gesture of farewell.
Now here's the real peach. In my opinion, this quote directly foreshadows Gatsby's death and is the main significance of the entire scene. The roar of the twenties and the din of the horns in the background frame the true nature of the host. He is isolated and empty. That is how he lives (through his parties and beyond) AND that is how he dies, ... isolated and empty. And the clincher is "his hand up in a formal gesture of farewell."
Farewell, indeed, Mr. "Great" Gatsby. Farewell, indeed.