Will he eat sandwiches cut into small fingers? Easy to eat, snack like and can put healthy filling like natural no added junk peanut butter inside. Good for protein.
Or how about sticks of cheese, favoured baby rice cakes, raisins, slices of banana? All quick and easy to snack on. And tasty.
If its healthy sweet alternatives then try some blueberry or banana mini pancakes. You can make a batch then freeze and get one out when needed as quick snack. Or sweetcorn and cheese pikelets.
My DS, 18 months, was always a good eater too and is going through a natural picky stage. Its very frustrating isn't it! These things usually work for him though.