I carry the normal tool box, plus hose clamps,electrical kit, pieces of hose and rubber. Air line repair kit. TIre repair kit. Extra bulbs, headlight and fuses and lots of zip ties!
I carry normal toolbox with wrenches,pliers,sockets,and a 3lb.hammer.Also carry a parts box with wire and connectors,hoses,belts,etc. which I havn`t needed for a while.The very minute I would leave any of this at home-it would be needed.You never know what may save you a 2 hr. wait for a service truck.Also carry a siphon hose (from past experience).Truck to reefer or vise-versa.