I fished from Glatos with Big Dave back in December and bigger flies were the order of the day.
Like Pete said, having some brighter colors to offer can make a difference. One of my go-to patterns was a size 2 clouser with flourescent pink bucktail wing - overall length about 2.5 inches!
Dave did very well with a modified gotcha using a long tan rabbit strip wing.
On really skinny water/open flats situations, a couple of larger weightless patterns could be useful.
Glatos was very nice - not a "de-lux" destination but clean, comfortable and plenty to eat if you're hungry.
If the wind isn't too bad, you will probably fish the Southern flats - Jewfish cays, Water Cay etc. Some of the most stunning open white sand flats I've ever seen and plenty of good sized fish. Plenty of big barracuda around so a spare rod rigged with wire leader is worth having handy.
On very windy days, you can still find good fishing in the nearby creeks. Unlike the mangrove creek systems in other locations, these seemed to have mosty good bottoms for wading, so you're not stuck in the boat if you feel like stretching your legs - or need chase a big bone through the mangroves