In case you're interested in favors that are relatively inexpensive and green, take a gander at GreenWorld Project. For just a few dollars, you can get a tree seedling in a reusable container, all tired with a ribbon.
A variety ribbon and cap colors to choose from.
My favorite favor was the Birdfeeder Tree. The container becomes a birdfeeder, and each one contains a small pouch of birdseed.
And to cut costs even more or simply personalize it to exactly your taste, they sell just the tree seedlings, for as low as $1.50. A quick trip to the craft store (I like Michaels), and you can inexpensively wrap them up any way you like.