FarmVille maker Zynga is the subject of much criticism - some of it deserved - but the social gaming company has done a stand-up job running in-game promotions to raise money to build schools in Haiti. So far, there have been two Sweet Seeds for Haiti promotions in FarmVille, where players could donate money buy purchasing special limited edition crops using Farm Cash. Those two promotions have raised over $500K for Haiti, and a portion of those funds went to build a school(s) for those in need.
There are rumors flying that Zynga is planning a new in-game Haiti charity event soon, based on this series of backpack and school supply images discovered by FVFan. Since there seems to be a progression in the images, we can only guess that this promotion will require you to collect items (maybe school supplies?) from your neighbors to fill up your backpack until it overflows.
Please note that these items have not been released yet, and there's no guarantee that they will make it into FarmVille. (Let's be honest, this unreleased stuff usually makes it into the game). Keep your eyes open (and your wallets ready) to help those in need in the near future.