I only used an 8wt but a couple of other guys took along a 10wt too for the tarpon. However, I only saw 1 tarpon in my 4 days fishing... and we tended to focus more on the bones, blue runner and jacks.
In my opinion - unless you reeeeally want to part with your cash - I'd use your 9wt for the bones and anything else which comes along.
Fill your box with the usual fly patterns but pay particular attention to minnows, which the bonefish seem to target out there. The guides there will try get you to buy/use gummy minnows but in my opinion it's not really cricket. They are lethal though.
I bought an Orvis bonefish line before I went, but it didn't really matter as it was stolen from my bag with my reel somewhere between London and Caracas... make sure you pay the small fee to have your hold luggage wrapped with cling film. I ended up using a line and reel the guide sourced for me... from the sixties. But hey, they worked reasonably well enough.
Buy lightweight, quick dry, long sleeved shirts, trousers or shorts, a good hat, and one of those stretchy neck bandana things that you can pull up over your face. Slip on rubber/neoprene flats wading shoes. Make sure to get a couple of those neoprene individual finger gloves for your middle and index fingers.
As much backing as your reel can take
And don't forget the mosquito repellent!
Good luck.