Thanks to “mbm” for the tip! Julien’s Auction House will be auctioning off the fedora Judy wore when performing her iconic “Get Happy” in Summer Stock (1950). The item is expected to go for anywhere between eight and ten thousand dollars. The auction will take place in Beverly Hills, California on December 3rd & 4th.
Here is the Julien’s website for more info (including an Edith Head costume sketch for Judy):