Using the word "lagniappe"

The word is I think best known to the world outside New Orleans from Mark Twain’s mention in Life on the Mississippi, and I was credibly informed forty-odd years ago that Twain’s description of its use still obtained at that time:

  We picked up one excellent word—a word worth traveling to New Orleans to get; a nice limber, expressive, handy word—‘lagniappe.’ They pronounce it lanny-yap. It is Spanish—so they said. We discovered it at the head of a column of odds and ends in the Picayune, the first day; heard twenty people use it the second; inquired what it meant the third; adopted it and got facility in swinging it the fourth. It has a restricted meaning, but I think the people spread it out a little when they choose. It is the equivalent of the thirteenth roll in a ‘baker's dozen.’ It is something thrown in, gratis, for good measure. The custom originated in the Spanish quarter of the city. When a child or a servant buys something in a shop—or even the mayor or the governor, for aught I know—he finishes the operation by saying—
  ‘Give me something for lagniappe.’
  The shopman always responds; gives the child a bit of licorice-root, gives the servant a cheap cigar or a spool of thread, gives the governor—I don't know what he gives the governor; support, likely.
  When you are invited to drink, and this does occur now and then in New Orleans—and you say, ‘What, again?—no, I've had enough;’ the other party says, ‘But just this one time more—this is for lagniappe.’ When the beau perceives that he is stacking his compliments a trifle too high, and sees by the young lady's countenance that the edifice would have been better with the top compliment left off, he puts his ‘I beg pardon—no harm intended,' into the briefer form of ‘Oh, that's for lagniappe.’ If the waiter in the restaurant stumbles and spills a gill of coffee down the back of your neck, he says ‘For lagniappe, sah,’ and gets you another cup without extra charge.

Wikipedia says the word entered Louisiana French by way of South American Spanish, with an ultimate origin in Quechua.

Growing up in rural southern Louisiana, we looked forward to an annual fair called Lagniappe on the Bayou and the meaning was given as "a little something extra." Lagniappe on the Bayou

I think that its popular meaning would still be some association with this famous old food fair. It now gives its name to restaurants and cook books throughout the south. Whatever the origins of the word, it was always little used, but the popularity of the annual festival gave it a new lease on life within Cajun culture and throughout the south.

I would say that you could use it today to describe a gift of food or alcohol given above usual and customary monetary compensation. To a babysitter whom you'd already paid and tipped you could offer a pie to take home as lagniappe. I think the fact that it is free food or drink is essential to meaning. Anything else and it might be something, but it isn't lagniappe.

I emailed my old Cajun friend on Facebook who let me know three things about a lagniappe. 1) after your business is done and settled and nothing more is expected from anyone you can give lagniappe 2) whether you are buying or selling you can give lagniappe 3) lagniappe is anything frivolous or decadent, but usually sweet or intoxicating.

Lagniappe mean a little something extra. You pay for two, I give you tree and say they's a little lagniappe, just cause that's the way I am, me.

One thing, I don't think I ever heard an article with lagniappe, so don't say a lagniappe or the lagniappe, just lagniappe.