Fete des Rois
To celebrate the Feast of the Epiphany on 6 January, after Christmas boulangeries sell galette des rois (translates to pastry of the king), flat round pastries that come with gold paper crowns. Inside the galette, bakers place a small object, usually a toy animal, so when cut one piece will contain it. The person whose piece contains the object is crowned king (or queen) and gets to wear the gold crown which comes with various privileges and obligations. Apparently the French president is not allowed to participate so a galette without figurine or crown is served at the Elysée Palace.
The Fete des Rois (festival of the king) tradition relates to the Epiphany, or twelfth night (as in the Xmas song): the end of Christmas, when a king (or three kings) brought gifts of gold, frankincense and myrrh to the baby Jesus.