I agree with mandalinn82--planning better will help you a lot!
Also, some fast food places are better than others. At Subway, you can get a healthy choice. Of course, you would be better off not having any chips with your healthy choice! And more restaurants are offering better foods--still, anything in a fast food restaurant is liable to be more food than you need.
Sometimes if I have no other choice, I will get ONE regular hamburger at a place like McD's. Not a Big Mac, not a Quarter Pounder, just the regular hamburger, with pickles and mustard, no mayo, no cheese. It has about 220 calories, which is about as many cals as I need for a lunch anyway, to be losing. I can have an apple and add another 80 cals.
NO FRIES. They are the path to disaster. A SMALL order of fries is also 220 cals--I can't afford that! I'd be hungry the rest of the day if that was all I could have for my lunch.
Why not think of things you can make yourself, or things you can have at home to eat for dinner--quick foods, if you're not into cooking. And what about taking your lunch? It's not hard to put together a sandwich and some fruit--get yourself a lunch bag that's insulated--things like that!
Just some ideas to get you started...
Jay