I understand and am living the same thing. I bought a safety first lock for the refrigerator and my daughter can now get into that. I did get one of those ball things that go over the doorknob and now she can't get into the junk-food pantry!
One thing to consider because although they are growing, they have relatively small stomachs, is to give him smaller, more frequent meals.
Let him help you "cook" (sometimes works, sometimes doesn't)
There are a few ways to help kidify food...let him play with it. One way is to get a set of cookie cutters. I know michaels once had a 101 cookie cutter set made by Wilton. Cut sandwiches out or just the cheese, bread and meat and let him put together his own sandwich like a puzzle. I even make mini meatloafs into shapes. One thing I do because my kids LOVE pancakes, is to put a quarter cup of pumpkin in a regular recipe (1 cup flour (half wheat, half white), 1TBSP sugar, 2 tsp baking powder, 1/4 tsp salt, 1 cup milk, 1 egg, 2 TBSP oil). Then I add about a half cup of chocolate chips. Because of the chocolate, I don't even give them syrup and they LOVE these pancakes.
The other way to make food more fun is to dip it. Get small packs of dips from fast food places..honey mustard, bbq, ranch and let him dip his veggies. Even make cheese dip or queso so he can dip his broccoli in it himself.
My daughter (Age 4) loves flour tortillas and will eat anything wrapped up in one. Give him one or two at dinner and let him do the wrapping. Otherwise, just have patience, this too will pass!
I can get preachy on you now and tell you that it might not be a bad idea to get rid of the junk food out of the house altogether. Your son somehow equates that kind of food with fun and obviously is obsessing about it if he gets up to get it at night. If your family needs a sweet treat, fruit is a great snack that you can offer to your son even after dinner as a dessert. Strawberries or blueberries with a little whipped cream, peaches too, or even baked apples with a little brown sugar (cheap).
Good luck and let us know what happens!