Swim suit, mask, regs, and dive computer in carryon, a large hard sided suitcase with BCD's, wet suits, fins, lights, etc., along with everything else to get it to 49 pounds gets checked. I could rent the equipment in the suitcase if necessary, but mask and regs I consider essential. My face is really hard to fit with a mask and while I trust my dive operator....I trust my regs/computer more. I read somewhere that dive computers in the unpressurized cargo hold could be a bad thing under certain conditions but have no idea if that is true or not.
I'm amazed at the "carry on" variations on the airlines. On our last flight back on American, there were people carrying on full sized luggage and cramming it in the overhead bin. You might check with the particular airline to see if a larger carry on might be allowed. With my travel luck, I'd get charged to $50-$100 oversize charge.
safe travels.
jay