In the past, a snack was anything under $4 that serves 1 person. We've gotten pastries in Epcot at the Boulangerie Patisserie in France, fruit cups, yogurt parfaits, hot oatmeal with brown sugar and raisins, Shortbread cookies, Candy bars from the different Epcot countries--as long as the serving size is 1.
So, I would imagine that you shouldn't have a problem getting a single muffin/bagel as a snack.