Nothing beats personal experience for knowing what you will and won't need to extract your vehicle on the terrain you travel on. However, there are some basics that everyone should carry, some stuff which is useful occassionally, and some stuff you may never use, but may save the day if needed.

Essential Recovery Gear
This is the minimum recovery gear you should carry on the trail;

Recovery Strap - 2" or 3"
D-ring Shackles (2) - 5/8" or 3/4"
Leather Faced Gloves
First Aid Kit
Fire Extinguisher

Do not use the cheap tow straps with built in hooks as they can be dangerous, get a good quality 2" or 3" recovery strap or 1" recovery rope, along with some d-ring shackles, 5/8" or 3/4".

Recommended Recovery Gear
Items that may make recoveries easier, and will make you more self sufficient. These are in addition to the Essential items above.

Shovel (full size or folding)
Tree Saver - 3" strap or 1" rope
D-ring Shackles (2) - 3/4"
D-ring Shackles (2) - 5/8"
Hi Lift Jack - 48"
Ax
Tool Kit
Clean Clothes
Hand Cleaner/Wipes
Tire Repair Kit
Flashlight

A tree saver can be used as a "bridle" to spread the load across two recovery points. Additional shackles are always useful, 3/4" shackles may be too big for some vehicles recovery points, so carrying some 5/8" shackles is not a bad idea.

Winch
Having a winch is a great recovery aid, but it can be even more useful by carrying some basic equipment with it.

Snatch Block (1 or 2)
Tree Saver - 3" strap or 1" rope
10' High Test 3/8" Chain (with clevis hooks)
Pull Pal

Synthetic line is far safer and easier to use than steel line, and well worth the investment.

Other Trail Gear
The list of what else you may need on the trail is endless, but some of the most common items you may need from to time are listed below

Receiver Mounted Shackle
Tree Saw
Brush Loppers
Flares
Auto Tire Deflators
Air Tank
Engine Oil, ATF, Diff Fluid
Spare Parts
Air Tools (requires air tank)
Comprehensive Tool Kit
Electrical Tool Kit
Bottle Jack
Axle Stands
Exhaust Jack
Large Knife
Old Car Mats
Water (5 Gallons)
JB Weld
Cable Ties
Duct tape
Assorted Nuts & Bolts
ODBC II Tool (or Programmer)
Emergency Rations (Food/Water)
Ratchet Strap
12v Power Source
Mag Mount 12v Flood Light

With experience you will discover what spare parts will be useful on the trail, but items like tie rods and half shaft assemblies are eay trail repairs and can prevent an early finish for the day. Spare parts are of little use without the tools to install them, so plan ahead and carry the correct tools to install the parts you carry.

Summary
It can clearly be seen that it would be quite easy to carry a great deal of recovery gear. While the above lists are not exhaustive, they do cover the main items you are likely to need on the trail. Proper planning is the key to what you will need to carry with you. If you are travelling close to home and not far from civilization, then you may not need to carry as much. But if you venturing off the beaten track, then the more recovery gear, spare parts, and tools that you carry, the more likely you are to be able to drive your vehicle off the trail, should something go wrong.

A cell phone and other communications device, CB/FRS, is obviously very useful and a GPS may prove to be a life saver one day.

When extracting any vehicle, careful attention should be paid to safety, keep all bystanders back away from the area, and think everything through twice before you do it. Better to have a stuck truck, then someone injured.