How long of a distance?
PSP has a lot of things that can keep you entertained during long distance trips.
It's got internet, DVD playing, games and music and stuff...
Really it all depends if the trip's just long enough to say, beat a few levels in like Mario or something, or long enough to watch an entire feature-length movie. Cause if it isn't THAT long of a trip, then really you're just using your money on some features you may hardly ever use.