Can you get sick from eating a chip from someone else bag of chips?

Sure. Even if your hands are clean, it doesn't mean every bodies are. In Shopping Malls, the hand rails in escalators are loaded with bugs. If you touch the rail, forget to wash your hands and then touch food... you've got a chance of getting sick. The usual culprit is gastroenteritis bugs. Some people just don't wash their hands after going to the bathroom!! There is also viruses spread by coughing and sneezing. A good tip, I carry a small bottle of sanitiser everywhere with me; so I know I've got it covered.