You need to think about food before work. Prepare snacks you can take with you that you can eat at your desk. There are healthier choices than chips. How about apples slices, almonds, dried fruit, strawberries, healthier crackers.
Stuff your purse/desk with healthier choices so you are not tempted to get chips etc. I don't go anywhere without a bottled water and nuts or meal replacement bar in my purse. I don't want any Mcdonald's cravings to get the best of me LOL