My main line of thinking is short lift/tyres, possibly bumpers, provision for carrying spare gas/parts/water/&c, and recovery points with gear inside somewhere. Add in a few other "basics" - flares, blanket, non-perishable foods, and some sort of two-way radio - always assume you might get stuck out in East Nowhere, but plan on coming back. There is something to "worst-case" planning, believe me.
If you lift 3" or more without doing a BB, toss in sway bar discos for maximum articulation, but keep the sways for on-road duties.
Increase electrical capacity, to anticipate lighting and a winch.
I'm just cranky, but get real steel wheels if you don't have them already - I've bent steels out in the boonies and they can be made servicable with a hammer in a pinch. Not a perfect job, but it can get you back to civilisation.
Shovel, ax, hammer.
OBA or a portable air compressor.
Fire extinguishers (again, I'm cranky. Minimum 2x5# bottles.)
A DECENT first aid kit. I know the store-boughts are better than nothing, but those are for papercuts and bee stings. Build a low-grade trauma kit and KNOW HOW TO USE IT!
Operator upgrades ---
Mechanical know-how - not only general stuff, but enough to do your mods yourself (even if you don't) and know how to strip down any major assembly.
First aid know-how - I said it before, I'll say it again. Know how to use the stuff in your first aid kit. The life you save may be your own.
Buddy system - I leanred this way back when in Demo school - "Two is One, One is NONE." Backups and buddies, can't live without them. Get used to pairing off. When you go out, always let someone know where you're going, when you'll be back, and have a "drop-dead" time for when you get home.
Orienteering - GPS units have batteries. Batteries die. Know how to navigate with a compass. Know how to navigate WITHOUT a compass. Most of this can be taught in a day or so, check with the Boy Scouts for a course. Also, look for military manuals on orienteering.
Did I miss anything?
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