I have a different opinion -
IMHO, the refillable mugs at BW are only worth buying if you want a souvenir to take home. (I mainly use mine at work). The locations for refills are not very convenient - especially for morning coffee! And they really don't hold enough to make the trip to get the mug filled worth it!. (Picture me outside the BW Bakery gulping down 3 cups one after another, LOL). I like to travel to the parks as light as I can and hate to carry a mug around with me all day.
The villas all have coffeemakers. Bring some coffee and filters (basket type) and brew your own in the room. Better coffee, more coffee, and you can enjoy it while you get ready. If you also buy some paper cups, you can take the last cup with you on the way to the parks. No running down those Loooooong (LOL) hallways in your jammies to get some.
That said, if you are a Luna Park pool person and like to drink a lot of soda while you are there, the mugs might be worth it if you get a chair near Leapin' Libations. Otherwise, we find it more economical to just buy soda at the grocery and keep it in the refrigerator in the villa.
Best wishes -