I carry two first stages,one din one yoke, and a couple of 2nd stages, one mostly brass 109/56, my computer, my (empty) weight belt, a couple of small uw lights, a minimaist Zeagle bc, and fins, all in Crumpler carry on, along with my plastic bag of liquids (two bottles of defogger) a couple of lycra skins a 1mm suit, a snorkel and mask combo an my collecting net. Usually one fin , the Canon d10, compass, computer and gauges go into my significant other's carry on.
I mind losing things on the was back much less than the prospect of these essentials not ariving when I get to my destination. Shirts, pants shoes, I already have what I'm wearing A few ratty extras in check- through. My travel companion is gracious enough to allow me to displace some of her things so I can use about a fifth of her carry-on. I bring a small but efficient air pump and a good amount of plastic bags. The nets, airpump and the large box bags for shipping fish are not needed if you have no interest in collecting, or going somewhere that collecting is not permitted. I have no problems getting US Fish and Wildlife's permission and declarations because the director of the Newark office knows me well,(former student) and knows the regs, as they affect. 'ornamental live fish for personal use. Most customs agents will incorrectly try to apply commecial regulations to your little bag of fish because the don't really understand many of the regs themselve, regs that do not require you to have a permit.
But I digress.
Some TSA/Customs agents have seen scuba items and scuba cameras a thousand times, and those who have not will generally accept your explanations, except for dive lights, wich they want to see come on when they push the switch.
Years ago (digression warning) I was bringing back a snake I had caught on Jamaica. It was and still is a beautiful animal. It's my avatar picture on this board. Going through Jamaican customs is much messier thsn US customs. "LAWD GOD DIS MAN 'AVE A SERPENT IN DE BAG. I had that snake for about 12 years, then I donated it to an AZA select endangered species project.
The trick is to pack very very carefully, as though you were assempling a puzzle Try a number of strategies. Put all scuba type items on top, so it does not look like you are concealing anything. Practice packing and unpacking because you may have to just that so after the carry-on is inspected and pulled apart in the process. Avoid bulges. Make the outline of the carry-on as flat as possible. Weigh it.
So I should be ok with walking right through.... 
I'm headed to Hawaii on United airlines... I packed wives dive computer, bottom timer and 2 complete regulator sets in my one carry on bag... What are the chances of them giving me a hard time...? Any advice would be nice to have...
