The first thing I bought was a large fire extinguisher. In the remote areas where I drive any fire would burn the rig to the ground, even in the cities where the "fire-men" might show up or might not.
-Also I carry about 20liters of drinking water in unopened containers
-Spares of everything.
-Long, strong zip ties are also essential for holding up broken bits til they can get fixed.
-2 ground anchor stakes, at high altitude or in the desert there is nothing to attach the winch to, and a hammer to pound in the stake.
-200ft of 7/8" rope with shakles for times when firm ground is longer than the winch line. Nice for river crossings too, connect it to the truck ahead or behind, just in case you need to get pulled out.
-Lots of spare hoses and an assortment of hose clamps and rubber cement for making hose patches.
-Spare lug nuts, losing a wheel stinks, but not having enough lugs to put it back on is worse. (Down here, thieves will steal all but your security lugs)
-Spare headlight bulbs, essential
-2 spare tires
-And of course, my Machete, with a file to keep it sharp.
Most of this I have learned the hard way. Unfortunately, I'm still learning. Onward into the darkness...