I'd just take the smallest 35mm body with lenses around 28/50/135mm and as much film as you can sensibly fit into your pack (after the essentials, obviously). Don't take anything irreplaceable or seriously rare - for example, my SMC Pentax 120mm f2.8 never comes out if there's a real risk of damaging it, I use the common-or-garden Pentax-M 135mm f3.5 for those times instead. In fact the 28mm f3.5, 50mm f1.7 and 135mm f3.5 with an MX, ME Super or P30 would make an excellent outfit for this.
It really comes down to what the primary purpose of your trip is. I used to do a lot of 4x4ing, on those trips I'd just take something fairly indestructible and two or three easily replaced lenses. If you're driving, and especially if you're leading a group, you don't get time for photos as most people don't want to stop every five minutes. The primary aim here was to explore as many of the unsurfaced rights of way as you sensibly could before you ran out of daylight/weather/enthusiasm, any photos resulting were a bonus. At less than walking pace (as you don't want to damage the terrain or your vehicle) it takes a while to get anywhere, but that's part of the fun.