I would say it would depend upon what exactly your 45k service was/what your next schedule service is.

If you're just talking about an oil change, it wouldn't hurt to go ahead and do it ahead of your trip. You will probably be due for the next service by the time you get to LA, and certainly would be due before you get back - so it would probably be easier just to do it beforehand. That would also give your mechanic a chance to take a quick look over before you hit the road and let you know if there is anything that should be done before you leave, that wouldn't necessarily be covered on your service schedule - i.e. at 47k miles your tires may be approaching the end of their usable life.

But if you're talking about anything more significant than just a basic service, you could probably wait until you are done with your trip to get it done.