I have a Long Ranger 18 gal auxilliary tank in my JKU. Install is simple for a stock 3.8 (they make diesel versions too.) The tank fits on the opposite side of the rear drive shaft than the oem tank. It works great. Here is a link:
http://www.thelongranger.com.au/jklongrangefueltank.html
Take a look at the AEV 10 gal tank. Mounted outside of the vehicle, no fumes or safety issues. Does require an AEV tire carrier though, but that isn't all bad since the tire carrier has a built in shovel mount and very soon to be available High-Lift and Pull Pal mounts (which can be ordered now from Quadratec.) There is a thread on this tank on page 1 of this forum. Also, AEV rear bumper, which isn't required for the 10 gal tank, carries ~7.5 gals of water, a nice reserve to have.
Between a Genright or Long Ranger auxilliary tank and the AEV 10 gal tank you have 1/3 of your required 150gals of fuel.
If you do go with that 100gal tank strapped into the Jeep, you will need a LONG syphon hose and a method of raising the hose. The bottom of that 100gal tank will be far below the Jeep's fuel fill.
A winch on at least one of the Jeeps or truck would be beyond wise. What might take hours and then require numerous repeat performances with a shovel can take minutes with a winch. You are fighting time. maybe your fuel burn is zero or near zero when you're sunk up to the axles or frame, but your water use either doesn't change or increases due to the shoveling effort.
A High-Lift and a ~20"x20" piece of 3/4" plywood as a sand base would be on my list, along with either the "official" High-Lift accessories to 1.) lift the frame if your bumpers are not set up for High-Lift use and, 2.) to lift tires rather than frame or the "unofficial" accessories (For example, a strong ratchet strap can often be used to provide a frame lift point and sometime to lift a tire is there is roome enough between spokes - but nothing is safer than the proper accessorries.)
Some sort of sand mats or trax would also be on my list. There are some light weight relatively inexpensive options available. I saw a set in Moab just a couple of weeks ago that would be perfect, I'll try to recall the brand.
A good tire repair kit would be on my list, along with a good air pump per vehicle. Read up on re-seating tire beads with a bit of gasoline, just in case. Rather than one extra spare per vehicle, maybe one extra spare between the two veicles. Then add some tubes and a tube patch kit or two as well. You can run tubes in tubeless tires and tubes patch easily. Maybe a better option than a +50lb extra spare per Jeep.
In another thread you ask about mounting a second spare tire. Since you are removing the rear seat I would suggest as a possibility one of those rear racks which span the rear cargo area. Then you could mount the tire on top or below and still have use of a significant portion of the cargo area.
Also, I have seen a rear receiver mounted rack that has an 8" rise. I think Warrior Products offers it. With that rack, which with the rise mounts high enough to not be a hinderance in most situations off road, you could mount the extra spare there plus fuel or water cans, tool boxes, etc.
BTW, I would have for my own use sufficient maps and navigation equipment to do my own navigating. I would als have a worse case departure/escape route planned if there is one. For example, "If all navigation equipment is shot and we are on X leg of the trip with XXX miles driven and Y amount of fuel we can turn and head (say) east and drive until we hit road Z ...."
JPK