None. I want to hear what's going on with the truck, and I want every bit of available attention given to what's going on around me. Driving 14,000 lb. vehicles with 70+ year-old brake and suspension technology, steering that's prone to harsh bump-steer impulses, no anti-locks, no air bags, nothing to cushion impact from the sheet metal inside the cab, driving a high-profile vehicle with a roof that'll crush flat like tin foil if you roll it (or even worse, canvas)... IMO Listening to a stereo shouldn't even remotely be a consideration if we want to protect ourselves, those around us, and our right to continue driving such vehicles. I absolutely love driving my truck. I'm not afraid to drive my truck. But, by God I keep a close grip on what could happen if I'm distracted (or the bimbo in the prius next to me is) and I do my best to drive accordingly, as we all should.