For DII:
Rotoflex
motor mounts
t-mounts
These are the three things that I've found break most often off-road.
If you are locked and/or 33"+ and running tough trails, I suggest carrying CV joint/axle shaft assemblies for both sides, hub nuts, and a big-ass breaker bar for 32mm socket. If you don't have CDL, you really should carry both assemblies. If you have CDL you can limp back in rear-wheel drive if you have to...a winch helps as getting off the trail in rear-wheel-drive may be problematic. If you don't carry a hi-lift, at least carry a handle b/c you'll need it if you ever have to pull out a busted CV. I also suggest carrying a jack-stand.
You should also carry thread lock, all fluids (including 90-weight), several shop rags, a hip flask, and Alice in Chains-Unplugged.