-Wide-brimmed hat
-Sun block - can be purchased in-country.
-Immodium
-Camelbak or portable hydration of some sort.
-Portable water filter - Katadyn or Aquamira, depending on
amount of time "off the beaten path".
-Flashlights - preferably water-resistant, if not -proof.
-Extra batteries for above.
-Camera with extra battery and memory card.
-Water shoes/sandals
-Day pack for towels/swimsuits/etc on excursions.
-Sunglasses

This is what I've got so far.