Namely, the most important pieces of gear; mask, fins and snorkel. Diving is about swimming, breathing and seeing anywhere in the water column and including the surface; especially in southern waters.
The tropical environment offers clear water, so consider a mask which has low volume for clearing, a black skirt to enhance visual concentration and proper fit to eliminate "weeps". Wide view is essential as is nose pocket for clearing. Make sure the material is soft silicone and that the strap buckle is simple and strong. Some plastic buckles break. I suggest the Ocean Reef "reef" mask as the least expensive, low volume, high quality mask. The most expensive would probably be the Scubapro "frameless" and just as good. Either of these are also excellent freediving masks which is a common activity in southern waters. Bring mask cleaner-new masks are devilish to defog.
Think about the amount of swimming in tropical waters. The Apollo "bio fin" will reduce air use, especially when swimming upstream. These are costly, look for discount. The sizes run large, so be careful. Find a cheap pair of boots and cut them to slipper size. Reduces leg buoyancy and slip on quickly. Off the shelf booties are also available.
Get a streamlined snorkel and wear on the left side of head or carry in some sort of holster while on SCUBA.
If you carry a spear, I recommend the JBL travel spear which collapses by unscrewing the segments. The JBL barbed three prong head is the best in the business.
The Trident "yellow" goodie bag is excellent for lobsters, etc.
Good luck.
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