Should you have any you do not need, you can sell them for cash in The Exchange and if you need one to enter a certain Gold Card tournament, you can purchase it, if you find one available. In order to be able to access The Exchange, you are going to need to upgrade to Cake 2.0. Once you are logged in, you will see the "Exchange" button in the Gold Card tournament lobby, which takes you to the marketplace.
And what is this good for? Well, apart from gaining access to these tourneys, Cake also hints that “with strategic buying and selling, you will find it's possible to make money on Cake without ever playing a hand.”
For more details, visit the official Cake site here.
