The official rules regarding the use of refillable mugs can be found here on InfoCentral.

Back to LeeAnn's question, we often use our snack credit for something that we can eat for breakfast. We always visit the Main Street Bake Shop when leaving MK after Wishes and enjoy something yummy for breakfast the next morning in our room. As long as you're fine with pastry for breakfast, it works.

LeeAnn, considering you'll have a car with you, you might make a stop at a local grocery store and pick up some good in-room breakfast fare. While there, pick up bottled water which you can throw in the freezer of your room fridge (if you're staying at a mod or deluxe). If at a Value resort, the water bottles can chill overnight with ice in your cooler along with your milk. I'd buy Parmalat milk as it won't go bad. Other things we buy at the grocery store, when we manage to get to one, are cereal, bread (I bring our favorite brand of peanut butter from home), jelly, bagels and cream cheese (which can hang out in the cooler) and fruit.

Magical Express continues to be complimentary; I'm not sure if it's necessary but the planner in me says you should set it up before you leave for your trip.