Trail ratings are set and maintained often with no official authority. It's an ambiguous and imperfect system in a lot of places. Luckily, the enthusiastic community governs the ratings and publishes them online and in guidebooks.
In well-developed areas, like Moab, the land management jurisdictions (BLM, state parks, and even national parks) actively maintain trail ratings and have them on all trail number markers. The gnarlier the trail, the more likely it'll have a big sign at the beginning, like this:
33's and lockers on both axels are a recipe for success. You're more than capable of tackling things up to 7. Black diamonds (8-9) are also possible, but bottoming out or sustaining damage could happen without light mods. I'd say you'll want some basic recovery tools for anything over a green.
Here's what you'll need for blues:
- A couple multi-ton tow straps. Only a few dollars at Harbor Freight Tools.
- Tire recovery. Get some MaxTrax recovery boards. These things are amazing. All you do is put them under slipping tires to get out of a bind.
- A basic winch. For me, I started out with a hand winch for $30:
- A basic tire repair kit to fix flats. If you get more than one flat, and you can't repair a tire, you're SOL if you only carry the stock spare.
- First aid kit. Always a good idea when far from places where emergency services can't get to you quickly
- A good electric air compressor and tire deflators. You need to let air out when you get to dirt for ample traction, then fill the tires back up when you get back to pavement. Tire deflators automatically let out air until they hit a preset pressure. Your 33's will take multiple minutes to default down to an off-road worthy PSI, so it's way better to not have to manually hold each schrader valve open, and constantly check the PSI.
- Fire extinguishers. A brand new Jeep is NOT going to catch fire, but why not have one? It's always a good thing to carry.
For yellows and blacks, I'd highly recommend a good bumper-mounted electronic winch. A winch is even useful on greens and blues, but more so for the convenience. A winch is often the fastest and best recovery tool, even when it's not required. It's amazing what a good winch will get you out of. If you have one, you WILL use it on blacks and occasionally on yellows. You'll be pulling people out that are less equipped on greens and blues.
The Wranger comes with a stock sport bar. Jeep makes sure never to use a roll bar or roll cage in their marketing because the sport bar is not a roll bar or roll cage. You can add some bars between the sport bar to make a roll cage. This makes rollovers significantly safer, both on pavement and off-road.