When you look at the menu at a cart or stand, there will be a logo next to an item if it is a snack option. The logo/symbol is a square divided into four like a four-aquare game board. There are 2 purple and 2 white squares diagonal from each other with I think a "D", a "P", a cup, and a hot dog in the squares. At our resort they also had "snack options" marked on the outside of certain refrigerators so that all in the frig were snacks.
At the candy store on Main Street (MK), the lady said that we could pick out any single serving item that was under $4. If something isn't marked, ask if you can use your snack credit. Some of the things we got for snacks were corn dogs, bags of cotton candy, pretzels, frozen lemonades, smoothies (really delicious), smart water, vitamin water, chips, ice cream sandwiches, ice cream bars, frozen bananas, pineapple spears, lollipops, fudge, pecan clusters. We were killing ourselves on the last day to try to use them all so my advice is to get what you want when you see it/want it and if you run out early then all the better to pay out of pocket. We had to use 16 snack credits in MK the last day. I bought an ice cream for a little girl in line behind us and you would have thought I gave her the moon.