It's been a while since I did the POrtes Du Soleil - I think 2001 was the last one.
Three of us took 6" travel DH bikes with two pairs of forks each - one DH and a pair of Psylos at 5" for more pedally rides. This worked out quite well - we did a week of XC ish stuff, then a week of hooning culminating in the Dragon DH race. We were able to swap between lift assisted XCish shenanigans and full on (well, not for me, for the other two) Dh type shenanigans in an evening.
* Spare wheels
* Spare cassettes, Mech and chain
* DH and XC lids, pads, flats, spds and assorted other armour
* Complete spare pair of brakes
* Bleed kits for the above, spare rotors and fluid
* 40t DH chainrings for the XC-ish stuff
* 2x spare pairs of tyres (one was large volume XCish stuff - IRC Kujos or similar)
* Spare seal kits and oil for the DH forks
* Complete toolkit, bike stand, tarp, sleeping bags, track pump, random other stuff.
If you have the space and are on a bit of a budget, bear in mind it'll be cheaper to carry spare bits over and back than buy a '98 STX rear mech for 50 euro when you're out there.
All this filled half a transit (well, 2/3rds of a transit, but as you know, Contents May Settle In Transit).