As many spares as you can take, if you’re driving. We used spare forks, couple of wheels, mechs etc. Lots of clothes, you’ll need them if it rains.
If it is wet, the harder trails are much easier to ride – some of the blue / green graded ones have very flat corners which are far too easy to slide out on in the wet, the reds / blacks are much steeper bermed and nicer to dig into.
Agree with Geetee about tyres, though amazingly the week we were there we didn’t have a single puncture! I also only used a single set of organic pads.
Mark at Riders Retreat is a top lad, and will usually be around to help you out with repairs and such – he helped one of our group strip forks, though it turned out the damper cartridge was shot.
**edit** yup, I’d still go dual ply, just for the peace of mind – if you’re mainly doing DH stuff you won’t be pedalling much anyway! Make sure you do Dans le Gaz on t’other side of Les Gets, I think that was my favourite track of the trip