I keep a compressible backpack in the back. For some odd reason, there have been multiple times where I find myself wanting to explore something beyond where the Jeep will go. I’ll then throw what I carry in the Jeep into the pack: headlamp, first aid, gloves, water, etc.
I always keep an air compressor, some extra valve cores, a few tire related tools, some work gloves, and a few basic tools, and both duct tape and electrical tape in the back of any vehicle I'm in.
Bit random but I have road flares and a flare gun that I had in my truck previously. May never need them but you never know. I also have a little multitool with a socket and various phillips/flathead bits on it. Planning to add a first aid kit of some sort soon