Try having a plain burger with lettuce and tomato, skip the fries. Where I worked before the "gut-trucks" had yogurt and apples, crackers and cheese, and stuff like ham and cheese sandwiches- if your trucks have those options try those. It might not be great but it is better than eating chips or chocolate or something fried.
Just try to have a good dinner tonight to balance it out and get back on plan tommorrow.
Planning is important, I didn't plan my lunch one day last week and something similar happened to me