In The Great Gatsby, who attends Gatsby's funeral and why is the attendance significant?

Only a small smattering of individuals attend Jay Gatsby's funeral, including a few servants, the West Egg post man, the minister overseeing the service, Owl Eyes, Nick, and most tragically, Henry Gatz, Gatsby's father. 

Nick appears to be the closest person to Gatsby, although he's known him only briefly, so he takes on the responsibility of calling round to the other people he would expect to attend. When he reaches Wolfsheim, it becomes clear that the gangster would not be attending the funeral in spite of their close working relationship. Perhaps this is because Wolfsheim would prefer not to be seen as an associate of Gatsby's. 

Nick also calls over to Daisy and Tom's home asking as to whether they will attend the funeral, only to be told they have left town with no forwarding address or set date to return home. It is implied that they are evading the investigation of Myrtle's death, as Daisy was the one to actually run her down in Gatsby's car.

Nick sums up the Buchanan's attitude and behavior well when he says, "they were careless people,” for they “smashed up things and creatures and then retreated back into their money or their vast carelessness, or whatever it was that kept them together, and let other people clean up the mess they had made.”

And of all the people to attend Gatsby's parties only one showed, Owl Eyes. The lack of attendance implies the transient nature of the American Dream and the valuelessness of material things. Gatsby collected things the same way most people collect friends, and in the end he was alone.

In The Great Gatsby, how does Gatsby's funeral contrast with earlier party scenes?

In The Great Gatsby, probably the biggest contrast between Gatsby's funeral scene and his party scenes is that nobody attends his funeral. By contrast, his parties are packed with people who do not know him but come for the free food and drink, as well as to socialize with all the other people who come to Gatsby’s parties. None of the people who were happy to partake of his hospitality when he was alive feel enough remorse or sadness over his death to attend his funeral.

Even Klipspringer fails to attend. In contrast, when Gatsby was alive, Klipspringer was always present. He not only came to all Gatsby’s parties but also ended up taking such advantage of Gatsby’s generosity that he essentially lived in Gatsby’s house rent-free. He is even referred to as Gatsby’s boarder because he is always around.

Gatsby’s funeral is a sad affair. This is not only because he has been killed at a very young age but also because it underscores how superficial his existence was. He wanted to impress people with his wealth and so he threw lavish parties but generally did not know anyone who attended. At one party, Nick innocently tells Gatsby that he needed to seek out his host to introduce himself and thank him for his hospitality. He is surprised to learn that Gatsby is the host, which underscores how little the party goers knew Gatsby and how little he knows them.

In death, not one of the people who were happy to hold their hands out for the free food and drink cares enough about Gatsby to show their final respects. This includes Daisy. She and Tom go off to Europe and cannot even be bothered to come pay their final respects to Gatsby, who essentially was the sacrifice for Daisy’s running Myrtle down.

Moreover, it is raining on the day of the funeral, which contributes to the morbid, dreary and intensely sad atmosphere of the scene. The only people to attend the funeral who really cared about Gatsby are Nick and Gatsby’s father. However, the funeral makes it clear that neither of them really knew the many who called himself Jay Gatsby.

Gatsby's funeral is the absolute antithesis of his parties, it can be argued that this is probably the most profound point of the novel. Fitzgerald juxaposes the parties against the funeral to force the reader to re-evaluate their own values. I think it is fair to say life in the 1920's was not what it appeared to be. Fitzgerald challenged American society to face the music...even if it was "The Charleston".