Bad food in the workplace is my nemisis! I chase it away, my co-workers know to not offer to go get me 'snacks' of KFC/TacoHell, whatever nonsense they are getting that day. I bring my lunch, and I'm forcing myself to go to the gym- every single day on my days off.
Happily, my gym has free classes, and I'm a big fan of them. If I'm working out by myself, I get bored and wander off- but if I plant myself in the middle of an aerobics class, I'm too embarrassed to leave early and seem like a wuss. Also, I have much, MUCH more energy when I attend the gym reguarly. It's a tremendous difference.
I've lost 8 pounds in three weeks, hurray me!