"For instance, the involuntary manslaughter charge is going to be hard to proof when the evidence that he was planning on going on the ride the same day is presented. "

I'm pretty sure you can get involuntary manslaughter for driving recklessly, crashing your car, and killing your passenger. Or failing to maintain your car properly, crashing it due to an avoidable failure, and killing your passenger.

If I'm correct and you can get inv. manslaughter when you're in the same vehicle as the victim, it shouldn't be too hard to prove when the person was only planning to be in the ride later.