*lagniappe

noun
A lagniappe (/ˈlænjæp/ LAN-yap, /lænˈjæp/ lan-YAP) is "a small gift given to a customer by a merchant at the time of a purchase" (such as the 13th doughnut on purchase of a dozen), or more broadly, "something given or obtained gratuitously or by way of good measure."

[2] It can be used more generally as meaning any extra or unexpected benefit.

The word entered English from the Louisiana French adapting a Quechua word brought in to New Orleans by the Spanish Empire.