Try to view food as a resource/fuel for your body and nothing more... Also it's ok to have Mcdonalds just portion the meals... A diet soda and plan hamburger isn't so bad for you. Take care of your body now and in 50 years your body will thank you for the decision you made.
It's definitely hard when that stuff is all around you like that. You could try bringing a healthier alternative with you from home. Something that really helps a lot is drinking a lot of water. Another thing that really helps is eating enough protein. No, the junk at McDonald's doesn't count as protein. They put all kinds of nasty chemicals in that type of "meat". It's far better to eat a healthier type of protein, like a cooked chicken breast. I do not suggest getting the bags of chicken breasts from the frozen section at the supermarket, though, because those are pumped with similar chemicals. Just the fresh stuff. Even a hamburger patty from home made with fresh ground beef from the supermarket would be far better than McDonald's. This would be a far healthier approach if you need to watch your weight and your friends don't seem to need to. Don't forget to bring a salad with your lunch. Just don't drown it in dressing. Some fat in the diet is good, and we can't live without some. A small drizzle of olive oil on your salad would be better. If you're watching salt, a healthy vinegar that you like also on your salad will actually help with the salt craving. This is a healthy way to make a vinaigrette. You can even mix the olive oil in vinegar ahead, but make sure you shake the bottle before pouring a little bit on your salad. Just make sure you don't put too much. You wouldn't like it if it was too much anyway.
McDonald's has some better choices now. You could try the fruit and yogurt parfait, the apple dippers, etc. When you get a burger, remove 1/2 the bun; that way you are actually eating only 1/2 the simple carbs you otherwise would. I'd also recommend that you leave off the cheese, as I don't think it's even "real" cheese. Opt for milk, rather than a soda - milk has a lot of protein, and other vitamins for very few calories.
I do agree with FurballsMom - a better option would be take along healthy alternatives. Carry celery or carrot sticks with single serving packs of peanut butter, for snacks; for a sweet treat, pack along a cupfull of grapes, an apple or a pear. Fill up on air popped popcorn.
Salads can get boring, so try wrapping your salad fixings in a tortilla or stuff it into a pita.
Make sure you get plenty of exercise.