I used to teach with a woman who did a unit on The Great Gatsby by F. Scott Fitzgerald. For many years, she would host a party and all of her kids would dress up in Gatsby-era clothing. It was a big production and the kids loved it. (And anytime you bring food, it's a BIG plus!)
I might suggest that you try to dress in style. I would focus on information regarding things that happened in the story to discuss, perhaps, how America is changing—touching on how Gatsby made his money; and/or how hard it is to know who you're dealing with— referring to Gatsby's roots; and/or, the war, etc.
There could be discussion about locations mentioned in the book. You might try to talk about the narrator (Nick), as if an imaginary friend had never met him, and things he has told you about life in Gatsby's "circle." Or you could create a somber setting, pretending that everyone is gathered either at Gatsby's funeral or the reading of the will, and recalling things that you remember, even asking the other students questions that they should have the answers to if they read the book.
Sounds like a chance to have fun with the story and do something engaging that will make the novel more memorable. Enjoy!