Hazel:
It's not about flash, but upgrading to a nice set of suspension seats in a 4x4 with uncomfortable seats goes a really long way toward reducing driver fatigue and increasing safety. You'll wonder how you survived with the rock-hard stuff with the spring sticking out of the middle once you experience a nice suspension seat on the trail.
And speaking of surviving, whether you're paying somebody to build a custom rollcage or buying a ready-made weld-in or bolt-in cage, one of the first modifications you should do to your trail Jeep is some sort of rollover protection with good seatbelts. Put your money into the areas that increase safety and leave the gimbaled cupholders and widgety GPS systems for last.
Trasborg:
I've not spent any real time in suspension seats, so I can't speak to that. My three favorite seats are stock late-model YJ, stock WJ, and early '90s GM S-10 Blazer seats. That is not the only way I differ from most magazine guys-I am still foolish enough that I want to drive my Jeep whenever I want to drive it. I don't want to worry about the weather or where I'm going. I want the Jeep to do well on-road, be able to go off-road, and get me home, too. No trailer queens for me. So I like my stereos, I need a top, I need windshield wipers, and a heater is a big plus, too. I don't want to be bored out of my mind, frozen, or soaked while I'm driving home. I don't put the Jeep on a trailer and climb into the tow rig for the trip home, it's all Jeep all the way for me.
Something I learned from a friend long ago, that I still live by today, is if the Jeep starts, stops, and steers, everything else is secondary.
Drivetrain
Cappa:
I can barely maintain sanity without fuel injection in off-camber situations. As far as carbs go, it's hard to beat the off-road performance of a Holley Truck Avenger, but EFI is light-years better. Anyway, when it comes to the drivetrain, it doesn't make sense to blow a bunch of money on a 500hp engine swap if you're planning to keep the stock tranny and axles. Make swaps that make sense and think in moderation. Oh, and I am absolutely sick of hearing about Hemi swaps. It's not even that great of an engine swap when you consider the cost. A Dodge 318/360 or GM engine swap is easier, more cost-effective, and simply makes more sense. Ultimately, you're paying a lot of money for the Hemi logo.
Crazy crawl ratios just aren't needed and sometimes they can hurt more than help if you find yourself needing some wheel speed in mud or sand.
Hazel:
A good off-road carburetor like a Q-jet or Holley Truck Avenger will get the job done, but if your engine is relatively mild, there's a lot of off-angle performance to be had with a simple Holley 2-bbl Pro-Jection system or other fuel-injection conversion. An injected engine will make it much easier to keep your engine running at angles and will slightly reduce the need for super-low gears on the trail.
Low-range options and opinions vary, but I think a crawl ratio somewhere around 100:1 is pretty good for a manual tranny rig, and 30:1 works for an automatic. I've never really found myself wanting more than 150:1 (manual) or 50:1 (auto). As for low-range T-case gearboxes and crawler boxes, they're usually worth the money, but I'd recommend waiting on pulling the trigger on this mod until after your axle gearing has been upgraded. You may no longer find the need with new axle gears.
Trasborg:
More and more I find myself looking to diesel engines for the powerplant of choice. Sure, a short-wheelbase, open-top Jeep with a V-8 is a great time, and I do love driving them. But I love the pull the diesel has from a standing start, the smell of the fuel and the exhaust, and the sound of the clanky fuel system under the hood. That said, I think every gas Jeep should be fuel-injected. Unless you are going for a concourse-level restoration, ditch that 19th-century tech and join the rest of the world.
I really like the low-range transfer cases for the heavy rock stuff. But I really don't wheel in the heavy rock stuff except for once in a great while. If I can squeak out enough time to go wheeling, I'm getting out of civilization to the open trail. Mud, desert, fire roads, rock-strewn trails, wherever people aren't, and wherever there is no traffic. Find me a weekend where there isn't a logjam on some boulder-strewn trail nowadays. So most of the time, a granny First gear in the manual gear box and a regular low gear gets me enough control for my rocks and I tend to use high-range for the mud and sand, if my engine has enough oomph.