I've always believed in having the right gear for the job in hand and learned the hard way. As a young man, the British government sent me off to cover a secret war in Borneo equipped (by them) with inappropriate kit. I had a Rollie 2.8E and 20 rolls of HP3 (that's 240 exposures), a Nikon F (50mm f./1.4 lens) with 20 rolls of HP3 (that's 720 pictures) and a fixed lens Kodak 16mm movie camera. The Kodak took a hit within a few days which told me that it was not a good idea to stand still and hold the camera steady whilst filming. Thankfully they had the good sense to send a group of men from Nepal to do the important part of the job, who made their own very effective weapons.
I then went to work for myself and bought kit that I thought was right. When I later undertook work for Penthouse Mag, Bob Guccione stipulated he wanted everything shot on Kodachrome so I bought a 35mm outfit for the purpose and still have it. (See picture)
Once I got into underwater photography (20 years later) I bought two Nikonos and two 15mm lenses and two flashguns (eventually swapped for two NikonosSB 104). I met Doug Perrine on a trip and noted that he had come to more or less the same conclusion at that time.
I then started on the painful route of housed cameras and lenses (and various lightsources), both with film and later digital. I would see what other people used during trips and make purchasing decisions accordingly. It didn't matter that I bought stuff I rarely used. That was when it was OK to check in 100kg with a 20kg baggage allowance! Times have changed. I have cupboards full of stuff bought and now passed over.
Thanks to information gleaned from people on this website I now carry a very slimmed down set of kit that is all carry-on. I have redundancy if disaster happens yet I also am equipped to take surface pictures too.
My assignments are always last minute so I have no luxury of sending stuff by cargo. I just grab and go.
I thought you might be interested to know what I now use.
Subject to change if new information comes to hand, I now take:
1 Sea & Sea DX housing with optical dome port (as good as the bigger plexiglass job I always swore by) and macro port.
2 D200 cameras (small enough).
2 Inon Z-240 strobes
1 Tokina 10-17 mm lens
1 Nikon 35-105 zoom with macro capability at 105mm
1 10.5 Nikkor (bought before the Tokina but kept for surface use and as a redundant lens for underwater use)
1 Macbook Pro (15 inch)
Wetpixel has allowed me to get it right (unless you know better) quickly.
I have not included incidentals so don't tell me I missed out the synch leads!