Wrap your parts in paper towels or rags, then vacuum pack in freezer bags with a squirt of oil inside.
That will keep the stuff from rusting away.
I carry a drive flange for the guys that blow factory lockouts, along with bolts/snap ring for it.
Basic hand tools, and the more compact the better, I don't carry the really big sockets (Except for spindle nut socket) and I don't carry anything really small that Jeeps don't normally use...
Jack handle has a 1/2" drive extension welded into it, so I don't have to carry along a long breaker bar, and with a common 1/2" drive extension/socket for lug nuts, I don't have to carry a different lug wrench.
A heavy walled jack handle also makes for a pry bar, large hammer, ect. in a pinch,
Mine is threaded on both ends, will accept tie rod ends as a 'Get You Home' steering link when needed. (Tie rod ends in the 'Spares' box)
An adjustable wrench with graduations on the side usually works for 'Backing' wrenches in most cases, where you need TWO wrenches to get something on/off, so that keeps the 'Extras' to a minimum,
Snap ring pliers that do internal/external and have different tips usually saves room,
Along with one of those '4-in-1' screwdrivers keeps the drivers to a minimum.
They will usually accept common tool bits, like torx, allen, ect. so that means just the bits instead of extra drive tools with bulky handles.
I take crap about my tool bag instead of tool box.
Bags don't rattle, the stuff down into places you have instead of taking up room other stuff could be using, and you can oil them to keep tools from rusting.
Tape a bulb and socket with some lead wire inside the top of your glove box.
Much less likely to get your 'Make Shift' test light broken taped to the top of the glove box, and it's always handy that way.
Wrap your flashlight handle with duct tape, electrical tape, 'O' rings, ect. that are for your Jeep.
The wrap will keep your hands from freezing on the light in cold weather, and we all know how handy tape can be!
Make your air hose out of fuel line with an air chuck in both ends.
With a quick turn of a screwdriver, you have extra fuel line and the correct size line clamps for your fuel system... JUST IN CASE...
Get one of those skinny ammo cans with a good waterproof seal under the lid,
Grease the seal with dielectric grease,
Pack your 'Extras' in that can, and bolt it to the back side of the PASSENGER FENDER or someplace under the body or on the frame where it's not 'Obvious',
Good place for extra keys, 'Keep Dry' parts you don't normally need often.
Ignition rotors and modules come to mind right away...
Well packed against impact and stored away for the day when you loose you keys or a rotor/ignition module gives up.