There are definitely times when you just need something quick, and unfortunately fast food is too convenient to pass up in these situations. The key though is to get as healthy of a meal as you can possibly get there. For example, if you must have a hamburger, have it without the cheese, bacon, or mayo. Definitely far from perfect, but you just saved yourself 300 calories and many grams of fat right there. Even better yet, instead of the hamburger get the grilled chicken sandwich (not the crispy one - that is just as bad if not worse) with tomato and lettuce, no mayo. By the way, do you know how long it takes to burn off 300 calories on the treadmill??
Don't EVER get the combo meal which just adds fat and sugar and empty calories. Instead, if you don't think the sandwich will appease your hunger, go for the cup of fruit or baked potato (no sour cream) and you should be good to go.
Finally, give up the sodas for good and stick to water and skim milk. It's not easy, as Americans I think we're addicted to sugar, but stay away even from juices, which are loaded with sugars. But once you get past that hump you'll ask yourself how you ever drank the stuff in the first place. Seriously, I don't drink anything now but water or skim milk. Every once in a while I get a random craving for a 7up or something like that. When I taste it, my immediate reaction is "wow that is super sweet" and end up throwing it away after the first sip or two.
Anyways, good luck, and all of us are here to motivate each other