Just back from BWV.
Staff at Boardwalk Bakery told me mug could be used at bakery, Seashore Sweets, Belle Vue in the morning, Boardwalk Joe's at night, pool, and pizza window (don't remember name).
I personally used mug at bakery, candy store (great cocoa), Belle Vue in the morning, and pool.
By the way, I felt funny not tipping bartender at pool but I had no cash on me as I left the room with just two mugs to get a quick drink. We're not supposed to tip on free drinks, are we? I just felt a little awkward.
Margaret in CT
PS Just before I left for this trip, I called BW front desk and they told me refillable mugs could only be used at bakery and pool.