Here is the remaining stuff you must have:
Good Cheers
Good Humor
comfortable clothes for 80F to 100F temperatures
sunscreen
mini pharmacy (aspirin, imodium etc.)
full size spare
working jack
tire repair kit
spare gas (a few gallons will do)
nylon tow strap (no metal hooks please)
cooler * for drinks etc.
drinking water (min. 1 liter per person per day)
drinks and snacks
provisions for lunch (day 1,2,3,4 and 6 - all other days restaurant lunch)
Here is what you could bring (not needed but fun to have):
still or video camera (bring enough film and batteries)
GPS
satellite phone (no cell phone coverage most days)
maps
books on plants or geology
camping chairs
foldable table
a handheld UHF/VHF radio
* Ice chest tip:
get a big conventional ice chest with block ice to cool. It is preferrable over actively powered ice chests - they need too much ventilated room around them and drain your battery over night