I lost 45 lbs. a couple years ago, and one of the major diet changes I made was switching from regular soda to diet. I'm still drinking diet soda, and the weight is still off. I do drink less diet soda than I used to. Also, I cut out drinking alcohol for the most part. I still have a beer or a glass of wine now and again.
I think if you're seriously committed to eating better, you do have to make compromises, or else you are setting yourself up for failure. One of my compromises was to make one weekend day a week my "bad day", where I could eat the fast food or whatever, so long as I'd eaten well that week.
cadre's suggestion of tracking what you eat is an excellent one. I've used both MyPyramid (for nutrition class) and FitDay (for personal use) and found them useful. Personally, I spent the money on a computer program called DietPower. I think it's easier to use. You can find a free 2-week trial at their website:
Calorie Counter Diet Software Guaranteed... Food Diary Try FREE.. It really helped to make me aware of what I was putting in my mouth, how much, and how often. These programs will also allow you to track your physical activity.
What's funny is that I actually eat more these days because I eat healthy food and exercise. Like Baraka, I also try to eat every 3 hours. I prefer to keep my blood sugar at an even keel; I can feel it now when it's out of whack. I don't eat a huge meal.
As for fast food--you should check out a feature in Men's Health called Eat This, Not That:
Eat This, Not That - The No-Diet Weight Loss Solution From Men's Health There are some good options out there, if you know what to look for.
EDIT: Baraka posted while I was posting. Exercise is vital! I too am curious to know what you do now for physical activity, Runningwater.