I use a Tamrac shoulder bag for my DSLR, three lenses for underwater (12-24, 60 and 105 micros) , one 85-400 telephoto topside and the Aquatica eyepiece. My iPad got in this bag as well. This weighs in at about 15 pounds. This goes under the seat in front of me.
I use an Akona roll on camera bag (no longer sold) for my Aquatica housing, 8 inch dome port, macro port, two DS-161 strobes, extensions, strobe arms, carry handle, sherpa strap, chargers, vacuum pump, assembly tools, and assorted small items. This is 38 pounds and goes in the overhead. I do admit to checking this on the return flight. The only problem experienced was learning how fragile an Aquatica eyepiece is and how expensive it is to repair, it is now in the carryon with lenses. I have had no problem carrying the roller on with Delta and US Air. With a small plane like a Twin Otter in the islands it has to be checked.
Regulators and masks with corrective lenses go in my wife's carry on.
Lugging this through airports can be trying. The best advice I can offer is buy no luggage without wheels or the ability to mount to the handle of a roller.