1. get all of that stuff out of your house. Replace it with healthy foods.
2. when he refuses to eat what you provide, don't give him any alternatives. If he's hungry, he'll eat eventually. No kid will starve in the face of food.
3. when he wants a snack later, give him one. Just have only healthy options on hand. Since it's not at the dinner table, the "issue" might not loom large in his mind and he will be more likely to try something different - as a snack. Snacks can be mini meals in disguise. Use this to your advantage.
4. don't take him to fast food restaurants. Don't take him to any restaurants, in fact, for a while, except maybe those vegetarian or healthy ones, or really different ones where chicken strips aren't on the menu. Try out Korean or Thai or other place. He will balk at first but when he sees everyone else enjoying themselves, and feels the growl in his stomach, he might try something out. If not, well, he can just eat a snack at home, later :)
5. keep him occupied at home for a little while. Don't let him hang out with his friends at their houses, because he'll eat with them and come home without an appetite. If he notices a change in his social life, just have his friends over at your house. In fact, if you have a friend or two over for dinner, he will be less likely to throw a fit in front of them, and he'll see *them* enjoying the food you put out, and be more likely to want to eat, too.
You'll do fine, and so will he. Within a few days or a week or so you'll see him eating things you never thought he would before. If you have some fights over this, keep your eyes on the larger goal: we are, after all, what we eat, and your instincts are correct. Your son needs to eat a healthier diet, or his habits will catch up with him.