Katy - I've traveled frequently with my kids, though luckily they are out of the diaper stage. My first question, are you renting a car in CA? If you are, of course the easiest answer is to pick up some when you're there. If that is not an option, I'd pack that box with you. Just take them out of the box to save weight, or just send the box through with luggage, with all your information written on it. If you pack them, we usually took an entire suitcase filled with diapers, wipes, etc along with usually toys. The extra room at the end of the trip is usually welcome with all the things you'll pick up. Remember each passenger is entitled to two checked bags, and if you've bought your baby a seat, that's two more bags!!! Since we've always bought the seat, that got us 8 bags (4 of us), so bringing that bag of diapers wasn't a problem. You're other option is to send the diapers to the resort you're staying at in CA, but you'd still have to figure out how to get them on-board. I'd either pick-up in CA or bring the extra bag.