And look I found the trinket!
A king cake (sometimes rendered as kingcake, kings' cake, king's cake, or three kings cake) is a type of cake associated with the festival of Epiphany in the Christmas season in a number of countries, and in other places with the pre-Lenten celebrations of Mardi Gras / Carnival. It is a popular food item during the Christmas season (Christmas Eve to Epiphany) in Lebanon, France, Belgium, Quebec and Switzerland (galette or gâteau des Rois), Portugal (bolo rei), Spain, and Spanish America (roscón or rosca de reyes and tortell in Catalonia).
The cake has a small trinket (often a small plastic baby, said to represent Baby Jesus) inside.
In most workplaces, the one who finds the trinket must be bought lunch once a month until the next year, when they must provide the King Cake.