The sun's rays in the tropics are far stronger than further north, and sunburn can occur much faster, especially during the hours of 10am to 3pm. Belize is a subtropical country with large tracts of jungle and marshland. Bugs love this kind of environment. Bring plenty of repellent. Fortunately, the Tradewinds keep the bug problem at bay most of the year, and the higher elevations and jungle lodges of Cayo are surprisingly bug free.
Many small aircraft have weight limits.
Pack a carry-on. Include a swimsuit, one change of clothes, basic toiletries and essential dive gear such as your mask, computer and regulator. This way, if your luggage does get lost, you're still ready to dive. Carry all your important documentation and valuables in your carry-on luggage or on your person. Carry a list of emergency phone numbers and addresses.