In terms of equipment, you need very little. Most equipment makes the vehicle more comfortable, more capable, more easy to use (both driving and camping), etc. In terms of basics, a couple of spare tyres, a shovel, a tow rope, possibly a kinetic rope, possibly an axe, a couple of jerry cans for reserve fuel, a jack, some sort of tool kit, some spares.
The next level which isn't absolutely essential but pretty important is a Cargo barrier - most travellers tend to load up their vehicles with kit, if you have a crash, its all coming forward. We hit a big pot hole, we had a very solid metal cargo barrier bolted in to the vehicle and it bent it with the weight of all the kit being thrown forward. One or all of us would definitely have been killed if it wasn't for the cargo barrier. I think its often overlooked and its important. Also possibly a second battery with some sort of control mechanism. Its easy to flatten your battery and especially if you are a solo vehicle, you could get stuck.
If you want to get into putting equipment on the vehicle as most travellers do - long range fuel tanks, upgraded suspension, better tyres, bash plates, bull bar, additional batteries, water tanks, window grills, roof rack, roof tent, ladder, tow bar, upgraded sound system, cargo barrier, the list goes on and on. For an idea of kit, ARB in Aus to a great range as Cruisers are far more prevelant over there and if you look them up on the web, it will at least give you an idea of what is available.