I haven't fished the Seychelles so no first hand experience. Anything that resembles the local forage (shrimps, crabs etc.) in form and size would be my choice. The gotcha and crazy charlie derivatives all work well because they are good general representations.
If you tie flies I strongly recommend taking a small tying kit along. It doesn't need to be the "kitchen sink" - just a plentiful supply of hooks in a range of sizes - small to large. Some craft fur, pantone pens, flash etc. a good selection of dumbell eyes and you have enough to come up with something close to the specifics of the particular island/flats you are fishing.
Think 'size', 'general profile' and 'sink rate' rather than specific patterns.
When sight fishing, look over your shoulder from time to time, you never know who's behind you