Owning a truck, you always gotta carry extra things than when you do when driving a car I think. You never know when you will have to haul something, pull someone out or tow someone outta nowhere.

Right now I just carry:

some leather work gloves
an assortment of bungee-cords
20 feet of small rope
2 1x15' tie down straps 1500 capicty I recall
portatable airpump/compressor
big flashlight