The zinc oxide if for where you miss with the sunscreen...
My self I just use Vaseline Intensive Care lotion when I get a bad sunburn (which happens more often than not even with sunscreen because my skin is so fair!!).
You might also want to bring some PeptoBismol (Bismuth) for stomach upsets.....most people are not used to eating/drinking all the great fruit and fruit juices available in the DR. and the excess Vitamin C can cause stomach upset.
It's a GREAT place to visit (the DR anyway-not sure about the resort having never been there....).
Look forward to beautiful weather,gorgeous beaches,spectacular sunsets, friendly people and lively music!!