There's no need to bring one.
There's been a Pack 'n Play in every DVC room (studio, 2 bedroom, etc.) we ever stayed in, including the Polynesian. A Pack 'n Play (and an appropriately-sized sheet) are on the standard list of DVC room amenities, so there should be one in your room, usually stored inside the closet. If there isn't, just call the front desk and ask for one.