Andy:
My rig is in my signature.
Here's what fit:
Ike housing
2 - 8" long, 2" diameter bouyancy strobe arms
2 - 12" long, 1" diameter bouyancy arms
6 strobe arm clamps (2-way)
1 strobe arm clamp (3-way)
2 strobe arm ball adaptors (to ike handles)
Fantasea Nano focus light with saddle clamp and ball head adaptor
2 - Ikelite DS50 strobes, with diffusers and ball strobe head adaptors
About 40 AA batteries (8 in the strobes, rest spares)
4 AAA batteries (in the Fantasea Nano)
1 4-seat AA/AAA strobe recharger w/ cord
Olympus BLM battery charger w/ cord
2 - Olympus E330 camera bodies
Olympus Zuiko 14-54 lens
Olympus Zuiko 35mm macro lens
Olympus Zuiko 50-140 lens
Ikelite 5503 (short 6" dome for macro) lens port, with neoprene cover and shade
Ikelite zoom sleeve and collar assembly (low profile for 14-54 lens)
Ike dual sync cord
Ike single sync cord
Handmade carry handle for rig (about 24" of rope with two brass shackles)
USB Card reader with short USB pigtail
Misc. memory cards (CF)
2 spare Olympus BLM batteries
Misc. UV filters and an ND filter for the different lens diameters (for abovewater use)
Plastic strap wrench (to help get dome port/extension separated for 8" dome, not included)
Misc lens cloths, spare o-rings, and Ikelite lube packs
...bag was still under 32 lbs (40 is the US carryon limit...or was, will have to check if that's changed).
Here's what didn't fit, and rode with the checked scuba gear:
Ikelite 8" dome port assembly with shade, neoprene cover, and extension (wrapped in my wetsuit for extra padding)
Ikelite 2-handle base for housing (all the way in bottom of bag by wheels)
A small 'holster' bag for the camera for walking around above-water.
Here's what didn't fit and had to go elsewhere (another carryon my wife lugged):
Laptop, laptop charger/cord, and ethernet cable.
12" leg "Gorillapod" (for abovewater)
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Basically only the laptop and charger were the main items I wished I could've put in there. Although the laptop would slip into the supplied pocket with everything else in place, I didn't feel comfortable with how tight it was (was afraid I was flexing the screen and chassis). And it was obviously 'expanding' the bag beyond the carry-on limit of about 9" height at that point.
The tray-base with handles and 8" dome wouldn't be sensible to put in anyway as they'd just kill way too much room for other stuff. I suspect if I upgrade to twin DS125s (eventually!!) I'll have to move at least a couple of the arm segments into checked too...probably keep the parts for at least one arm, although without the base I'd be shooting in natural light if my checked bag got lost in transit...
I guess the tray/handles can be disassembled for travelling, but I don't like to carry more tools than I have to, or worry about loose nuts and bolts - the 2 screws and rubber spacers in the base are worry enough.