I'd give him a good multivitamin, and be sure it has iron in it if he's drinking a lot of milk. I like the idea of giving him a probiotic -- you can also get the probiotic effect in live-culture yogurt. Be sure he doesn't have any kind of gagging reflex, that might keep him from swallowing comfortably in general, and then cut the chips and chocolate entirely and tell him that food is available, and keep offering it (healthy food) until he gets hungry enough to eat it. Even if he continues to refuse, you will at least be giving him the milk and the vitamin, to sort of help the situation. You can ease the ultimatum nature of this by varying what you offer from what he has seen before. My son is a pretty picky eater, but he likes things you wouldn't expect -- lentil soup with cumin, for example, and olives, pickles, broccoli, green peppers. But he dislikes a lot of foods often eaten by kids, such as pasta and cheese. So you might try spicing it up a bit.
Good luck!
May be a good idea to not buy or give him just choc and chips he can only eat them if you give that to him? There are some really nice cereals and pastas in shapes on the market, plenty of good finger foods, so place them infront and him and let him get on with it, maybe your concern is too much, I know we like our children to eat well but sometimes we can labor it and they do seem to go the opposite way, back off and see what happens ...good Luck
Sounds like he's craving foods that would feed yeast. Too much yeast in the body will cause one to crave sugars, carbohydrates, etc. and not eat nutritious foods at all. Has he suffered from thrush or been treated with antibiotics since he was born??? He might need a good probiotic. Doctors won't even bring up the subject of yeast and probiotics have finally started gaining popularity to keep yeast under control and help with digestion.