I'd be interested to see how some folks get all their dive gear in a carry-on. My wife and I each have a diver gear bag that weighs in at just under the 50 lb limit. Try as I might I could not get our BCDs, regs, fins, mask, snorkel, wetsuits and booties, SpareAir tanks, lights and batteries, save-a-dive kit, and all sorts of misc stuff like bug spray, sunscreen, de-fog. Maybe the simple answer is pack clothes as carry-on and rent gear...
I have a review on the board somewhere regarding the Generation II Dive Caddy.
Marci and I used them for a cave diving trip to Mexico and got every thing in including:
3 regulators (two for the primary sidemount tanks and one for a stage),
3 sidemount/stage kits for the 3 rental tanks,
a Dive Rite Nomad (not a small BC by any means),
XL sized Jet Fins (fins that are both long and wide with deep foot pockets),
a canister light,
two back up lights,
a 400' primary reel, two 125' jump reels and two 100' safety spools,
two Shearwater Predator computers,
mask and back up mask,
5mm one piece wetsuit, boots and aviator style dive hood, and
a swimsuit, a couple tee shirts and a towel.
Now, the qualifier here is that the Dive Caddy with all that in it, weighed 56 pounds, but would fit in the over head bin with the accessory bag removed (it becomes your personal bag) and with the accessory bag removed it was right at the 50 pound limit.
In comparison, for a tropical pretty fish single tank dive trip I will pack a double hose reg, a plate and 30 pound wing, a dive light, pair of computers, mask, XL Jet Fins, 3mm or 5mm wet suit and boots, a dive beanie and towel with plenty of room left over for shorts, underwear, tee shirts, toiletries, etc and it becomes a single bag trip - all in the carry-on.
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I also look at things differently. On a cave trip with 3 high end regs, two computers, a spendy can light, reels, etc I have about $5,000 worth of dive gear in the bag and I AM NOT going to check it, or rely on the hope of available rental gear at the destination. In contrast, tee shirts, shorts and basic toiletry items I can buy almost anywhere for around $50 and get through a week long dive trip. Replacing dive gear will cost me 100 times as much and there's no guarantee I could even find it at the destination.