Don't drink the water. Bottled and boiled water are used at the camps. There are no convenience stores, and even the best lodges don't offer much. Bring batteries, a surge protector for any sensitive electronic gear you might have and extra supplies of any medications. Estimate how much film you'll need, then bring twice as much.
Film is hard to find.
Bug repellent, sunscreen, a well-ventilated hat. Get the best pair of binoculars you can afford or borrow, and a heavy-duty but lightweight flashlight. You don't need serious hiking boots, but your shoes must be comfortable enough to walk in for hours. Weather varies from cool mornings to brutally hot afternoons to cold nights. Bring clothing you can layer.