The number one extra has to be practice:
To help simulate casting from a casting platform, place several hula hoops up at 30, 40, 50 and 75′. Stand on a cooler and try to put the fly into the hula hoop with a maximum of two back casts. Try this with a weighted fly, think Clouser, with the point clipped off and with a larger more air resistant fly. Do it with the wind and without. I place a taller step ladder behind me about where your guide will be standing and have even leaned a tall pole up with it to give a bit more realism. Perhaps the hardest cast will be where you use your backcast as "the cast" at times necessary in order to get the cast off with the wind coming over the wrong shoulder and no time to reposition the boat.
Other than that remember the little things
such as lip balm with sun screen, fresh sun screen, spare camera batteries and a few zip lock bags to protect cameras, phones, etc. I wear glasses so a small glasses kit complete with screwdriver and spare screws and a cleaning micro cloth rides along, as does a multitool and a bit of cork oil/reel oil for my reels. I place the eyeglass kit in a Tupperware sandwich keeper with a spare croakie, and side shields and a small bottle of eye glass cleaner. The reel kit goes in a similar Tupperware keeper.
I always carry
a very light weight wind breaker/rain jacket along or if nothing else one of those throwaway slickers that folks up to sandwich size. A sudden storm and wind can leave you cold even in the tropics.
Salt is hard on rods, reels and lines
but a good cleaning each evening will keep things in ship shape. I strip the lines off to the backing and rinse well with warm water and then as I reel them back on I do so through a line conditioner applictor. When rinsing rods, use a toothbrush
to clean around guide feet and the reel seat. Don't forget to rinse off pliers, and any other gear that gets wet with salt spray. (sun glasses for instance)
Anyway, have a great trip and be sure to give us a report.