Simple and straightforward:
* The bakery gave me a lagniappe of a delicious chocolate chip cookie with my purchase.
* My grandmother always gave us a lagniappe of candy after a visit.
More elaborate:
* The local market surprised us with a lagniappe of fresh herbs and tomatoes, a delightful bonus to our grocery haul.
* After the concert, the band played a lagniappe of their most popular song, sending the audience home with a lasting memory.
Figurative usage:
* The extra time we spent on the beach was a lagniappe, a delightful bonus to our already perfect vacation.
* The unexpected promotion was a lagniappe, a rewarding surprise after a year of hard work.