I know the FJ Cruisers use about 2/3 tank to get into the springs (about 12 gallons), then we have done about 4 hrs of ride and drives and top off with 5 gallens to get out. That is what we have used the last two years. We have toped off at ice house as well before we left. Hope this helps, now the german's 4/runner with the 1kzt only used about 1/4 tank to the springs and not much more on the way out. Anyhow it is all how much you idle the truck inbetween the obisticals and how much you wait for broken truck and slow vechicles on the trail. Having a extra 5 gallons never hurts, but that said, there is usually some around to ask for at the springs if needed(and some people do ask for it to get out). The first year, I had my 80 with all it fuel capacity (69 gallons) topped off at Ice house, I supplied 4 fjs with fuel and me (there stock tanks) and two days of ride and drives on the fuel and we were not on fume, but close( so 4x17= 68 gallons and 69 gallons = 137 gallons for 5 truck = 27 gallons each) funny math but you may get the point. Last year each Fj used about 22 gallons with only 4 hours of ride and drive to get throught the trail. Good luck on the choice.
As for water, even though I want to only have a gallon a day for each day, I used more like 1 and 3/4 to 2 gallons/day water for all the walking and stuff I did. Getting out and spotting and working the trail. And I wanted more at time. So that said, it is high mountain, with a very dry climate that can suck the moisture out of you. Think about what you want and add some more for just in case(iho).
I remember wheeling the first year with the 80 with full fuel tanks, almost 40 gallons water, a rear diff for the Fj and 2 CV shafts and extra food and gear for the crew. That was one heavy beast on the trail. It was a great experence to see what a 80 could do with all that weight.
Good luck with the choices. later Robbie