I don't really "watch" what snacks I eat at WDW as even though I drool over the pictures of everything on the DIS, once I'm there I find I don't really want those big, heavy cupcakes. I do enjoy a cinnamon roll (or two!) from MK bakery but that's usually breakfast. The one snack I LOVE to get is the Itzakadoozie popsicles from the carts. Not all of the carts have them but I get one whenever I can find it.
The dailyplate.com has the Giant Itzakadoozie popsicles (which they definitely are at the parks, they're huge!) listed with 100 calories, no fat, and 24 grams of carbs.