Hi there! First thing: I believe sodium and sugar may be addictive substances! I used to LOOOOVE cheese fries, and now I do not even WANT them. Not at ALL. In fact, I don't even want ANYTHING fried. I'd have to be absolutely starving and that be the only thing available. I promise that if you stick with it for awhile, those cravings WILL go away.
And please know that fast food CAN be healthy! Most fast food joints are offering a lot of healthy options, like grilled chicken sandwiches and fruit cups. Just make sure you nix the mayo or whatever else they might slap on there. Fast food salads can be great too... just beware of things like croutons, crispy noodles, and dressing. I like to pour the dressing out on the SIDE and dip the tips of my fork in it before each bite. You get just a LITTLE dressing in every bite and you end up using much much less.
And remember that you CAN eat ANYTHING you want... in small portions. Craving french fries? Get a junior fry and a chicken salad. Dying for a burger? Get just a single burger or cheeseburger, but get a fruit cup instead of fries. Don't know about McDonald's sides, but Wendy's has mandarin oranges that are really good.
If you're craving pizza, get pizza! Just have a slice or two at the most - and a salad. Or better yet - lean cuisine pizzas are really delicious!
Come up with at-home cooking alternatives that you like. You can find healthy alternative recipes for just about anything online.