Setbacks are a part of life. Someone will bring in cake for a coworkers birthday. Your special someone will surprise you with dinner out. You'll have to work late. You'll get sick. These things happen. Just because you have an unperfect moment doesn't mean the entire day or week is lost.
I use the tips I've found on SP to combat everyday speed bumps. A surprise meal out is fine. I just ask for a to-go box right away and put half the meal away before I start eating. Working late is a bummer, but I will do wall push-ups, squats, and lunges on my bathroom breaks to get some exercise.