If he is a bit hooked on sugar (and the foods listed way back near the start of the thread are high in sugar or simple carbs), then he may well crave high sugar foods and feel 'hungry' for them but not better foods.
Loads more protein, loads more complex carbs, far less sugar/simple carbs..
Give him cheesey scrambled eggs on whole grain toast, with some ham, a yoghurt (live, not filled with sugar, avoid the 0 fat ones they are packed with sugar) and a piece of fruit for breakfast.
Make sure when he has sandwiches, they are mostly filling and very little bread - thin sliced bread or medium sliced, rather than thick sliced or big fat rolls/buns - fill them up with ham, egg mayo, cheese, etc rather than a single slice of ham or a thin layer of cream cheese..
Just don't have crisps, biscuits etc in the house - if they are not there, they are not an option, end of.
Make him a clock with meal times and snack times marked on it, so he can clearly understand EXACTLY when these will happen.
I would change the rules on a day when you and he are super busy with things that will engage and distract him, because if he IS craving sugar and his blood sugars are rocketing and crashing, the first few days of having much less sugar are going to be pretty hard for him.