Headphones
I know in MN it's illegal to wear headphones in a car. Not sure about on a bike, but I'd be surprised if it was different. That being said, I've done it a few times on the freeway. Can't usually hear much anyways at that speed so it didn't bother me. To be safe though I used the ear buds and only put one ear in. For me the biggest reason not to was it hurt. My helmet is snug enough that the ear bud would make my ear sore after about 20 minutes.