I have been to the Seychelles twice now and am going again at the beginning of March.
The flies that you need for bonefish are gotchas and crazy charlies sizes 2-6. Some Shallow H2Os. Clousers in various sizes. The bonefish coming onto the flats on a rising tide will take almost anything. I have caught them on 1/0 clousers.
You can catch Trigger fish with merkins size 4. In fact it is worthwhile taking a lot of merkins as there are a lot of other fish such as emperor fish in the turtle grass that take merkins. There are also permit around.
For blue fin trevally basically anything will work.
For Giant Trevally you can take poppers, baitfish patterns like Decievers size 2/0 and also big clousers size 2/0 and 1/0.
For milkfish you need a special algae fly which looks like a hook dragged through pond weed. If you want info on this let me know.
Remember to take lots of leader material and spare lines as the fish coming off the coral flats will wrap the line around coral heads and you may loose the complete fly line.