Heavy Duty Duct Tape, BFH, HID Flashlight (Good One, Surefire equivalent), Bungee Cords, Tie-Down Ratchet Straps, Emergency Blanket, Food Rations (Cliff Bars), Water, Motor Oil, Antifreeze, Brake Fluid, Tire Gauge......I can keep going.
I use a milk crate. Keeps it all organized, at my fingertips, and it doesnt roll or slide around the backend of the truck.