You have a number of options regarding how you and the game handle your Charm collection. The controls are found on the "My Charms" screen.
Click anywhere in the Charm Display area (shown above) to open "My Charms"
The "My Charms" page displays your Charm collection. Scroll up and down to see everything, including your used up Standard Charms (displayed as black silhouettes.) Click "Charm Settings" to modify how your Party Favor Charms are auto-equipped, or turn that feature off entirely.
Most players prefer to use the Charm "Auto Equip" feature, which automatically replaces used up Party Favor Charms with the next most valuable Party Favor in your collection as you wager. In some cases, players prefer to save this or that Charm for later, which is where the Charm Settings come in.
Standard type Charms, the kind you purchase just for yourself, cannot be set to Auto Equip. Those sorts of Charms must be equipped by hand. Just click on the Charm you wish to activate.
This account has all the different Charms set to be Auto Equipped (the default), but if this player wanted to save Creepy Cakes for later, for example, the player could simply remove the check and the game would no longer auto equip that type of Party Favor Charm. If Auto Equip Party Favors is unchecked, then no Charms will Auto Equip at all.
As new Party Favor Charms are purchased by and gifted to your account, those Charm types are automatically added to the active auto-equip list. Example: If you had selected only Martini Party Favors, and are then gifted a Shortcake Charm, Shortcakes get added to the types of Charms that will be auto-equipped. They may be unslected again using the Auto Equip Settings.