Hi Kevin,
There are so many snacks to get at WDW with the dining plan that it would be too difficult to list them all. A good rule of thumb is that most snacks that have retail prices under $3 or $4 are covered. When you go to a counter service restaurant or food stand in WDW their menu will indicate exactly which items you can buy with your snack credit.
In my experience I have seen items like the following available at different establishment;
A bottle of water, premium ice tea, soft drinks, or fountain soda
Popcorn, churros, ice cream, frozen banana treat, crispy rice cereal treat, a candy apple, block of fudge, cupcake, piece of carrot cake, ice pop, frozen lemonade, hot pretzel, candy bar, bag of potato chips, pretzels, mixed nuts, piece of fruit, fruit salad, bowl of grapes, yogurt, carton of milk, bagel, breakfast danish, bowl of dry cereal, chocolate eclair, yogurt, jello, applesauce, different types of muffins, big bakery cookies, chocolate covered marshmallows on a stick, hot tea, drip styled coffee, brownies, key lime pie, orange juice, soy milk, hot chocolate, etc.
I think you will be pleasantly surprised by how much different items you can get with the dining plan.
Also on page 3 of the
Disney DIning Plan brochure you can find an overview on how the snack credits work.
Hope that helps answer your question. Enjoy your trip - Michelle