Trucks look good with wide stripes. A 10 inch stripe kit or a 12 inch stripe kit will work well on any full size truck. Smaller trucks can go with a 10 inch or an 8 inch stripe kit. For trucks that want to stripe the hood, roof and tailgate a 30 foot kit is fine. If the truck has a hard bed cover then a 36 foot kit will provide more material. The best thing to do is measure the areas you wish to stripe and then purchase a little more material than you need.
The truck above used an 10 inch stripe kit and added 1/4″ pinstripes.