My son used to be so fussy but luckily he's not keen on chocolate or crisps. Here's some tips I have that might help
Putting 6 slices of cucumber into a cheese or cheese spread sandwich. He might not notice the first 2 slices when he bites into then pick the rest out
A pear cut into stick like shapes, easy on the palate and sweet
Carrot waffles from asda, sneaky veg!
Crushing an age suitable vitamin into his milk
Low sugar cereal bars and breakfast biscuits along with a cup of milk if he won't eat a bowl of cereal
50/50 bread or wholemeal
Cutting up 6-8 cherry tomatoes really small into pasta sauce
Making meals a picnic to start with. Crackers, chunks of cheese, bits of cold meat, carrot and cucumber sticks, cut up fruit
Teaching him that the sweet thing comes after the main thing. An ice lolly after his lunch, a pudding after dinner
Leave him to eat and spy through the door. If he isn't being watched or getting attention and learns what is there is it basically, he may well tuck in
Investigate if it's textures he has an issue with and only offer small amounts of food with the textures he doesn't like
Makes sweets a weekly thing
Swap crisps for lentil or root veg crisps. You can't taste the difference with some of them these days
If he's a chicken nugget and chips type kid, that's ok. Just as long as he eats a varied diet this meal