The next bag of Funyuns you buy might earn you a Spring Llama in FarmVille. Players of three of Zynga’s most popular social games are about to be rewarded for snacking on Cheetos, Ruffles, Dortios, and Lays.

Frito-Lay and Zynga have teamed up for a promotion that allows Facebook gamers to unlock prizes in FarmVille, CityVille, and CastleVille by purchasing certain snack-sized bags of chips. Players can purchase the specially marked bags at WalMart, and once they’re done munching they must enter a code into the Game Card Tab on the specific game on Facebook.

There’s a different prize for each game and for each different bag of chips. For instance, a FarmVille-labeled bag of Ruffles nets players the “Chip to-go Bistro” while a CityVille-marked bag of Cheetos gets you a “Brilliant Beach House.”

Also part of the promotion are Zynga gift cards, in the amounts of $15 and $25. Buying those will also give you access to a special item. But it you pair a gift card with the codes of 4 out of the 5 participating snacks, you can unlock a “Super Item.” For FarmVille, a Spring Pegacorn; For CityVille, a Glowing Glass Condo; and for CastleVille, a Red Knight’s Horse.

Speaking of food and Facebook social gaming, last month we told you about a new reward service that awards Facebook credits for eating out at various restaurants. Plink allows you to sync up your credit card so whenever you slide it at a Taco Bell or a Quiznos, you earn credits that can be used toward items in CityVille, Mafia Wars, and more.

As Zynga expands promotions and attempts to make nearly everything and Facebook credit-earning opportunity, they might also have something else in mind. CEO Mark Pincus recently said that he thinks Zynga and online gambling is a “good natural fit.”

The Frito-Lay promotion will run from March 1st to April 12th. Here’s a full chart of what you will get from each snack: