Since I have extensive UW-photo equipment to carry (first MFT, now FF) there is (almost) no more space for scuba equipment in the carry on luggage (camera rucksack plus a camera bag)...
Scuba equipment that goes in carry-on: TCs and compass.
Only part of the photo equipment goes in carry-on: camera, lenses with zoomgears, flashes, Li+ batteries (!), optical viewfinder for UW-housing, macroport, close-up diopter for macro and laptop. In addition traveling documents and something to read while on the plane...
The rest of scuba gear and photo-gear (including housing, domeports and WACP-C in padded travel bags) goes into two hard-suit cases for check-in and is stuffed/enveloped by clothings etc. as good as it is possible (not much weight left for luxury accessories as clothing, toilet articles etc...
)...
In addition I wear a
big fishing vest when travelling, so that I could stuff from the carry-on in the vest, in case there would be a complaint by the airline personal (so far never was required, but carry-on was weighted already several times)...
Wolfgang