How autobiographical is the The Great Gatsby? I think Nick shows some similarities to Fitzgerald
The perspective on wealth and its trappings and particularly the way that people who were born into it acted is certainly a common strain in both Nick's life and F. Scott Fitzgerald. Both had the experience of being around wealthy people but lacked that same level of wealth (though they were both comfortably well off) that entitled one to looking down upon "new money" or those who had to work for their wealth.
The setting for the story also mimics part of Fitzgerald's life as he spent quite a few years living on Long Island and writing about the antics of the people there, similar to the way that Nick chronicles the parties that Gatsby throws and the behavior of the people at the parties.
The sense of being an outsider is also one that may have origins in Fitzgerald's own life as he never felt very successful while alive due to the fact that his writings weren't particularly in favor until after his death.