I also have a long hour, stressful job (in fact, I am posting from there at 7:15, so that might give you an idea). I also have a half hour commute each way.
I have four ways to stay on track:
1) I WANT it (as the people above described). I want it so bad that I can pass up that cookie, that free lunch, and have learned to embrace hunger and not nibble on whatever comes my way. Until you get there, honestly, almost nothing will help you.
2) I go to the gym at lunch. I talked to my boss and explained what I wanted to do, and he and I agreed that I can take a little over my hour for lunch if needed as long as I make up the hours (which I more than do). I found a gym w/in 10 min of work and I shower before coming back.
3) I pack a cooler and take it to work. It has an icee to keep it cold, and a bunch of salad makings and healthy fixings. I don't have time to make lunch in the morning, and I have a desk job, so I keep a plate and knife and fork at my desk and I make my lunch and eat it at my desk as I continue to work after I get back from the gym. It almost always includes a dinner-sized salad, some form of protein, and some fruit that I can cut up and nibble on throughout the afternoon.
I also keep some non-perishable meal-type items in my desk just in case I forget (soups, hormel meals, etc).
4) I track my food. Every single bite that goes in my body. I use sparkpeople.com, which is free and accessible from everywhere. I put my exercise there too.
As far as planning goes, I also keep my gym bag in my car and stock it regularly. I am notoriously late in the mornings and that way I don't have the "I don't have time" excuse.
Oh, and I don't eat "diet" food. I just eat food and track it. I do 1200 calories and am constantly surprised at how much food I can pack in there!