as silly as it sounds, i consider this to be an important issue. i have read on some reviews that they recently have not been filling guests' cups at brb. i specifically called superclubs who put me on hold and called the resort. i was assured that they would fill any cup i brought. i have been to brb before and find it immensely difficult to believe that they would not fill my mug. if they didn't, one of the first orders of business for me would be to go directly to a manager to make sure that it wouldn't happen again - and i am quite confident that they would allow it. i have stayed at three different superclubs properties in jamaica for the last four years running (twice at gln, brb and hedo 3) and they have always been great and accomodated any request i have made (request even more demanding than simply filling a mug). besides, you have already paid for all the drinks you are going to have, so why would they care whether you have 3 small drinks or one big one? it also cuts down on the number of mugs they have to wash and collect from the beach - which the employees have to take time to do every day - so it makes sense for them (far less labor intensive).
now to answer the original question. before my first trip to jamaica, someone gave me the advice to take my own mug. of the numerous "tips" i got regarding travel to jamaica, it turned out to be the most useful/practical one. it has added more enjoyment to my vacations and allowed me to relax more than most of the other advice i took. i know that sounds extreme/weird, but it's true. not that you won't have a great trip without it, but you will wish you had taken one along if you decide not to.
anyway, those are my thoughts...