I find the standard Defender heater on mine is more than substantial, leave it on for a bit and it's like a furnace. Anyway, I would have a decent set of AT or mud tyres (31" is a good size to have without lift). In no particular order:
Tubular bumper (orignal bumper can get bent easy)
rock sliders
Decent exhaust system
A good service
LED lights are a good shout
If you like music, a good pair of speakers with a subwoofer (one with a built in amp if you don't want anything extreme)
Good mats and some sound proofing.
Spare wheel carrier (back door soon gets warped with heavier tyres / wheels - i learnt the hard way)
If you plan on any substantial off roading, a locking or limited slip diff in the rear will do wonders. Better off spending cash on that than fancy flexing suspension.
CB radio if you plan on doing group stuff
Good battery(s) if you want to get a winch.
If your suspension is original (I.E been with the car since built) it might be worth replacing the springs and shocks as they can sag over time. Bearmach do good springs, though be sure to check the rate. A good all round shock is Bilstein. Good point to change bushes too.
that's some to be getting on with
