Last year around this time when I was in Paris my friend introduced me to this French new year tradition. Saturday I was able to visit the French Bakery in north Provo before we left Provo. I bought a $28 King Cake for Buffie to share this tradition with her friends. The one from Paris was from supermarket and cost lots less. The Provo one should be much tastier. Check out this article on the tradition to see which way you would like to treat the person whose piece of cake contains the trinket (a small ring for the Provo one), just search King Cake or Galette de Rois in google e.g.:
http://www.askoxford.com/languages/culturevulture/france/galette/
http://en.wikipedia.org/wiki/King_cake
Cheryl who worked with me till I moved to my current job. She grew up in France. She said that the trinket used to be something edible. But since often the treatment of the finder of it was to sing or to buy a round of drinks for the crowd, the finder often preferred to eat the bean and not tell anyone. That is why now it is made of something not edible so the finder has to “spill the bean”. 
Buffie let us know how things turn out.
