Don't have any sitting around in the office.
If you don't have a bag of chips or box of pretzels in your desk, then it is harder for your to mindlessly snack or eat if you are in a bad mood. This way, you have to be conscious in your meal planning for the day.
Double extra bonus points if you put your food for the day together the night before after you've eaten dinner, or in the morning after you've eaten breakfast. Why? You aren't as hungry, so you'll pack sensibly sized portions. And if you did it after breakfast, it means you actually ate it!