How to stop over eating?

sometimes when im stress i over eat. i tend to grab a pastry or munch on chips and cookies. i really want to stop doing that. i go to the gym and stuff but i want to maintain a healthy diet. i want to know any tips on eating healthy like what does it involve. i heard meat and cheese are bad for your digestive system. but i honestly didnt know since the world has its opinions on about anything. any suggestions on how to eat normal and what to eat for breakfast,lunch,dinner,and snacks>???? =]