Hi there!
Have a wonderful stay at Pop Century! I case you haven't noticed, Chip & Dale (who will be one of the opening CM's) has posted a lovely description on the resorts brd. It's a very big thread, hard to miss!
I'm sure there will be refillable mugs at PC as there are at all the others. The prices & sizes very. At CR, our mugs held abt 12 ozs, at WL, they hold 20. There is even a 64oz mug at Coranodo!
Generally, you purchase them in the food court. You can refill them with soda, coffee & ice tea. Some resorts might vary slightly. At CR they also had frozen coke. The price at WL in Sept was $12 per mug. I think it's a great value. We had at least 1-2 cups of coffee & 2-3 soda's per day. Also, you can only fill them at your resort, not in the parks. (Though, some folks do take them & get ice water from the vendors. Ice water is free at the parks.)
There is a huge debate on where you are "allowed" to use them only during your stay or if you can bring them back. I stay compeletely OUT of that one!!
Enjoy your stay!!