Following up our how to hack a coke machine coverage, here's a video on how to hack a snack machine. It's pretty much the same idea. Pay for something, but hold the release flap up on the bottom so the machine thinks it didn't drop your food. Then mash on the coin return button to get your money back.
Simple and unethical. Just the way you like it.
How to: Hack a Vending Machine? [TechEBlog]