Well so far I haven't done too much trail riding, mostly desert riding, and messing around, so I'd figure that I would ask the professionals before I go out on the trail, what are some necessities?

So far I've thought of:
-Jack
-Spare Tire
-Fire Extinguisher
-GPS
-CB Radio
-Extra Can Of Gas

Food
H2O
Parts that you have had a problem with in the past and a simple set of tools.

Chris had a good list around somewhere.

First aid kit

Heres my list, its pretty extensive and you dont really need all of the items but it would be nice to have

Peat sorb ¼ gallon
Duct tape
Electrical tape
Fuses 80piece
Magic marker
Tire plug kit
JB weld
RTV
Waterproof matches
Radiator hose repair kit
Hammer 16oz
Rags
Open/close end wrenches 22pc
Allen wrenches 48pc metric and SAE
Torx bits 19pc 1/2in drive
Needle nose pliers 6in
Wire brush 3pk
Screw driver flat and Philips 8 in 1
Road flares
Emergency fan belt $
Tire gauge
D-shackles
Vice grips 7in
Ratchet straps / Bungee cords 12pc
Zip ties
Collapsible container for catching fluids
Haynes manual
Electrical repair kit
Funnel