If you are talking must, then the answer is nothing. Stock standard the Patrol is still a beast. Just make sure everything is in good working order. You do not want to get stuck in the middle of nowhere.
Also, any modifications you do make, can reduce your reliability, so be careful before you spend.
In terms of suggestions:
1. The rear bumper on the Patrol is relatively low and can be prone to damage going down steps. Probably not the worst idea ever to have that in steel. Then while you're at it, add a swing arm for the tire. Pretty soon you are going to want bigger tires and all that weight on the door is not a good thing.
2. The LWB of the patrol limits the crossover axles a bit, so a suspension raise is probably not a bad way to go. (2" should be enough, but 3" and 35" tires just look s much better :) )
3. If you do not already have a spare fuel tank, consider one (or even another rear bumper swing arm for jerry cans) before doing long overland trips. The Patrol is thirsty and sometimes fuel can be scarce.
4. Even though the Patrol is tough as nails, it never hurts to have some extra protection (such as rock sliders and bash plates).
5. Cary some basic spare parts such as fuses, fan belts, bolts etc and a few basic tools. You never know.
6. Fire extinguisher and first aid kit. Things can get hairy and you would best be prepared.
7. Big tough and rugged tires.
8. Two-Way radio to talk to your friends while driving.
9. Basic recovery gear is never a bad idea.
10. Seat covers. It gets dirty, and you'd best protect what s yours.
Those are basically the only suggestions, but then, there are the toys as well:
1. Front bumper. You will probably never need it, but hey, it looks the part, and you can even put some spotlights and a winch on it to help out your buddies when they get stuck.
2. Refrigerator and freezer. You need to keep the meat and drink cold don't you?
3. Rear drawers because no-one uses the fold-up seats, and when you are fully loaded, it just makes getting to things easier. It also allows you to add some rails for that freezer you just put in.
4. Extra battery and inverter, because hey: why not have electricity available wherever you go. You never know when you might want to do something with it.
5. Roof rack and rooftop tent. Because once you get there, it might just be nice enough that you want to stay.
6. Built in kitchen with custom side windows. because camping is awesome, especially when everything is readily available and there.
7. Side awning. Once you use that built in kitchen of yours, you just don't want to do it in the sun.
8. Front lockers. Because who doesn't want to show off on the worst obstacles possible?
9. Snorkle. Sometimes you get into deep ... and you'd like to feel safe knowing some clean air is going through your engine.
9. Sound system. The neighbors want to hear your music too don't they?
10. Turbo, because towing a caravan at 120 just isn't enough. Might even be handy when you do the dunes, and doughnuts are fun.
11. X-Link and sway bar disconnects. It is just awesome when one wheel is more than a meter up on a rock.
12. Solar panels, so you can go really far. (Just remember the fuel).
13. Decals and/or paint, so you can look the part.
14. A decent camera, so you can prove you were there.
Did I miss anything?