In my opinion the necessary truck accessory items to carry are:
(These should be a part of the standard equipment list of every 4x4)
Shovel The most important 4x4 truck accessory.
Always keep a shovel handy!
Hi-Lift Jack 
A hi-lift jack is also the easiest way to remove a tire. It can sometimes be a delicate balance, so take precautions!
Carry a block of wood as a base if the ground is loose.
CB Radio
A CB radio makes communications between people in other trucks easier. It connects everyone traveling together forming a single group.
Here you can get a complete CB radio and mounting kit.
Tow Hooks Your truck needs to have a place to fasten the recovery straps both in front and rear. Even if you never get stuck yourself someone else might!
Recovery Strap
Usually the quickest way to get a truck unstuck.
The best recovery straps are elastic and help transmitting the force of the moving truck in just the right amount. Tire pressure gauge
When airing-down its important to use a tire pressure gauge to keep the pressure even among the tires. Same is true when pumping air into the tires later. Tire Pump A powerful tire pump is necessary to fill the tires after airing-down.
It can also be used to put the tire back on a wheel if it falls of the rim.
Tire Repair Kit
Instead of carrying a huge spare wheel and tire its often possible to fix even large holes in tires with a tire repair kit. Here you can get one of the best. Fire Extinguisher
Just remember to learn how to use the fire extinguisher. You never know when you are going to need it. First-Aid kit
In the outback's a doctor is not always easy to call. You should always be prepared! Carry a first-aid kit (and take a hands-on course) or buy this survivor kit. Toolset You need at least a hammer, crescent wrench, socket set, pliers, screwdrivers and work gloves.
Common spare parts Among these are: Oil, grease and common fluids, hoses, belts, bearings and u-joints.
Items vary depending on your truck brand.
The NICE-TO-HAVE's 4x4 truck accessories include, but are not limited to:
(It is often enough if one 4x4 in a group carries one of these)
GPS receiver When the visibility is low or the terrain unknown the best way to locate yourself accurately is a GPS receiver. I would recommend a handheld device with 8 channel multiplexer that can be connected to a computer. Laptop computer The laptop computer comes in handy for communicating with the GPS, collecting tracks and routes.
(Also good to watch DVD movies while the others are stuck) Spare tire For longer trips a spare tire may come in handy and the tire repair kit will not do. Telephone You have to check the availability of local phone systems. In Iceland and the Scandinavian countries we have NMT phones. There is seldom adequate GSM connection in the outback's.
Satellite phones work around the globe but are very expensive. Pinch Bar For testing the depth of a river or snow. A pinch bar comes in handy in other situations as well. Welding Wires If something breaks it is often possible to weld the broken parts temporarily together. Jumping Cables Jumping cables are necessary to help a truck when the battery is low. They also come in handy as you can connect two batteries together for welding. Pair of Sunglasses If you do not have welding glasses, two pairs of sunglasses is the next best choice.
Winch
For an extreme stuck a winch or two can work miracles. If possible use an extra truck as an anchor for the one using the winch.
