The simple answer is pack light! Just your dive and camera gear and a couple of T shirts and a pair of shorts. It's the tropics!. Wear your slacks and warmer clothes on the plane. You can always throw a jacket over your shoulder and put it in the overhead locker. You should be able to put most of your camera gear in a carry-on bag and keep it under 7kg.
The camera vest idea sounds OK until you get weighed as well! It happens with smaller regional airlines. Having your dive bag offloaded is a real pain. Keep your checked bag under 25kg.