I don't think healthy food is too much of an issue at our parks. Typically, you only buy one meal (Lunch) and if you are buying sweets etc, it's because you want that food, not for sustenance.
If I'm eating park food, it's a cheat meal, and you can eat a healthy brekky and dinner when you get home.
At MW you can get sandwiches at the Main St Deli, wrap at Village Bean, and the build your own burritos at DHB has lean grilled meat and plenty of vegetables and salsas served with it.
There's a Village Bean at WnW too, but WnW only has a couple of food outlets anyway.
At DW, they've got sandwiches at that sandwich bar, and at Green Bean, and I guess you could eat at the Buffet and stick to healthier options there.
At SW, there's Village bean, that healthy food place at the top terrace near the entrance. I don't know the menu well enough at dockside, but another option is just to eat at the Resort.
As for drinks, well water is literally the most ubiquitous option since just about every gift shop has a small drink fridge. Anything else has sugar (Except maybe Bepis Max / Conke Zero) Please nobody say juice bar is a real option. Thats basically a liquid meal, and not what you get when you dehydrated and want to quench yourself.
PS, I want parks here to sell the old style non fizzy lemonade like you can get at the US parks...That was my go to item.