Punta Cana is ocean diving yes?
it's been said, but i think emphasis should be put on safety equipment.
-SMB with a reel or permanently attached 10m of cord - learn how to deploy it as well... you won't look like an idiot if you ask the Dive Leader if you can deploy it the first few times to get the hang of it, when you really need to deploy it you want to be able to do it without increasing your stress level. This can act as a surface flotation device if needed as well... i can't personally stress the importance of having one, even if people disagree with me.
-small LED torch (make sure it's a diving one, not a water resistant one!)
-surface whistle and mirror
-under-water noise making device... tank rattle, banger... it doesn't matter what just something that will make noise [only!] when you need it to. this can also be done by tapping your knife on your tank if you have one.
dive computers are useful, but if you're having toured dives then hiring one (to make sure the dive leader isn't sending you into deco) isn't a bad idea.
nice to have is exposure suits. If I'm diving in warm water i like to wear as little neoprene as possible, boardies and 1mm L/S rash vest, i use and love sharkskin branded stuff. if there are stingers around a 1 or 3mm full length is optimum.
other than that, just fins, boots, mask, snorkel. if you're a vacation diver hiring the BCD and regs is probably fine.