Andrew, I've been twice on fly trips. It's incredible.
Best to expect that there is nothing there, coz there pretty much isnt. There is a couple of general stores, but there is not a lot in them.
Take some cash for tipping.
Be self sufficient for tackle.
Take some basic tackle to leave with the local's, they really appreciate it eg spools of mono, hooks, sinkers, old lures, jig heads etc.
For boots, try bites, patagonia marlwalker and simms flatsboots and sneakers. take wading socks and gravel guards if you can, you really gotta look after your feet over there.
Take heaps of sun screen and protection, the sun is harsh.
Take emodium (particularly at the mini hotel), panadol, anti histamines etc.
Dont drink the tap water, or clean your teeth with it.
The guides get a few japanese GT and jig anglers thru. I was last there in 08 and there werent many sounders on the island then.
Some of the guides arent proficient at speaking english but understand it fine, a smile and common courtesy goes a long way with them.
You'll have a ball, wish I was going on that trip.
