The trinkets in the cake is something very common in Ireland for Halloween. We put various items into a fruit bread called a barm brack, each of which is supposed to indicate the fortune of the person who finds the piece. A ring would indicate a romantic liaison looming, a rag would fortell poverty, etc. This site
has some extra information.
In France the tradition is to eat a Galette des Rois
during the month of January. Originally this 'King's Cake' was eaten for the celebration of the Epiphany - the day when the three magi arrived at the stable in Bethlehem to venerate the baby Jesus. The cake always contains a fève
or bean. The bean has nowadays been replaced by highly collectable porcelean figure (like these
). The person who gets the fève is crowned king or queen for the day. Coupled with a very tasty puff-pastry, frangipane-filled cake it's a guarantted success.