I use a similar approach to PatW. I pack 2x Inon z240's, arms, battery chargers, batteries, Sola 500, macro ports, 4" Zen Dome, housing handles, macbook power supply, vacuum pump and dive computer in a Porter hard case (
Porter Case). The rest of my gear (Canon 7D, Nauticam housing, 60mm, 100mm, Tokina 10-17, 8" dome, macbook) go in a Think Tank backpack. These two bags are carry-on.
The dive gear and clothes go in checked luggage. In parts of the world where I'm strictly limited to 1 bag, I'll check the Porter and carry on the Think Tank. Depending on the situation, I also wear a photo vest and can stuff that with lots of things such as strobes, lights, battery chargers. I usually carry on enough so that if bags are lost I can take photos. You can usually rent dive gear but camera gear is not so easy to replace in a pinch.
The Porter case is worth taking a look at. I really like the dolly aspect of it. I can carry all of my gear using this setup without any help.