Lagniappe
Via Wikipedia

A lagniappe (pronounced /ˈlænjæp/ LAN-yap) is a small gift given to a customer by a merchant at the time of a purchase (such as a 13th donut when buying a dozen), or more broadly, “something given or obtained gratuitously or by way of good measure.”[1] The word is chiefly used in the Gulf Coast of the United States, especially Louisiana.[2] The word entered English from Louisiana French, in turn derived from the American Spanish phrase la ñapa (‘something that is added’ ). The term has been traced back to the Quechuaword yapay (‘to increase; to add’). In Andean markets it is still customary to ask for a yapa when making a purchase. The seller usually responds by throwing in a little extra. Although this is an old custom, it is still widely practiced today in Louisiana.