Not where I wheel! No cell service, too far out in the stix. 2-meter for help, CB for Jeep-to-Jeep communications
You have to be on mountain tops to even consider a bar or 2
Totally agreed. And, if you're going to have a ham rig of some sort in the Jeep, keeping a repeater guide for the area that you're travelling in handy would be a
very good idea. Most decent radios will let you scan through whatever bands they may cover, but that's only useful if someone happens to be talking on the repeater at the time you happen to be scanning; same applies to PL tone scan.
If you're going to rely on your radio (ham, CB, or otherwise) as oh-s*** communication, as others have said you'll also want a GPS unit. Telling someone "I'm about
x number of miles up Buttcrack Hollows trail" isn't necessarily going to get help straight to you - but giving latitude and longitude will. Consider that if you're really out in the back end of nowhere a helicopter may be sent out to spot you and guide people on the ground to your location, so accuracy counts for a lot.
One thing I've been doing for the last couple of years is keeping a copy of the repeater guide and the US Army Field Survival Guide on my phone as a backup to print. There are obvious downsides to this (battery goes out or the phone breaks, you're SOL), but it's at least one way to have the information to hand.
Back to the original question for a moment, though: one thing I haven't yet seen mentioned are the classic axe/hatchet and shovel combination. They may not be tools for working directly on the Jeep itself (until frustration sets in, anyway), but if you're running a D35 and find yourself suddenly needing to keep the wheel against the axle tube, that axe can be worth its weight in gold. Ditto ratchet straps - used them on three occasions to keep snapped leaf springs together enough to get the vehicle off the trail.