I was with Old_Man when his rear axle went south. 4 hours to get him to the point that he could drive out. My 4lb hammer was invaluable that day!
In addition to basic hand tools I carry at least 10 sticks of 6011 welding rod, welding gloves, and a hand-held welding face shield. Why?
Two different rigs with broken parts on the same day that had to be welded back together. Bubblegum and bailing wire were not an option. Here's a few pics of one of them...
My trackbar last year....
A LCA that sheared in half last year...no it wasn't on my heep!
Staightening out the slug that was used to align the 2 pieces of the LCA. BFH was put to good use.
It took 3 batteries in series to get enough penetration....and 3 pairs of dark sunglasses.
The best tool to carry and use properly to prevent serious injury or worse...your brain. When your junk breaks...Stop, look, plan your repais before you start turning wrenches or swinging a hammer.
I'd like to make one more suggestion if I could.
Learn how to do basic and/or intermidiate repairs in your garage BEFORE you hit the trail! The last pic of me welding was on a huge run (38 rigs total) and right after fixing this guys rig another driver snapped a front ale u-joint and that took out the ears on the shortside inner shaft. The driver "What do I do now?" and we all said "Change it it out." His response was "Okay....how do I do that?"
Myself and one of the guys I wheel with had his rig fixed in under 15 minutes once we found him a loaner shaft and u-joint. OBA made it a really quick job too.
As far as weight is concerned, common sense is your friend here folks.
Do you really need a full set of 6 point and 12 point sockets?
Do you really need a full set of 1/4", 3/8", and 1/2" drive sockets?
Do you really need a full set of Standard and Phillips screwdrivers?
How about wrenches.... Box end, open end, and ratchet wrenches?
Think about the tools you use frequently, that's the ones you should be carrying. Talk to the guys your wheeling with and make sure you aren't all carrying the same tools, share the load and cover all the bases. One guy brings sockets, the other guy brings wrenches, another brings misc. tools, etc, etc.