You could go many different ways with this sort of project. Jay Gatsby is a man associated with several images, so there are a variety of ones to pick from, many used as actual symbols within the narrative.
The green light on the end of the dock is the most obvious, representing Gatsby's yearning for Daisy and the money-mad world she represents.
Several objects within Gatsby's mansion could also represent his wealth. There are his fine shirts, which Daisy weeps over, and the pool in which Gatsby is ultimately murdered. Both of these are items Gatsby procures after gaining all of his money. Ultimately, neither does him much good. The shirts alone are not enough to entice Daisy. Gatsby only swims in the pool once, when summer is over and he knows Daisy will never be his.
Gatsby's car, with which Myrtle is run over and his fate is sealed, is another good option. The car's gold color obviously represents wealth and being a car, it also represents freedom.
Champagne or other alcoholic beverages might be a good choice. Gatsby got his money from bootlegging, a lucrative criminal activity in the 1920s. The image of alcohol could also be linked to Gatsby's parties.