I think this is the question that photographers get asked more than any other. I actually find it slightly offensive - as if the only reason I've managed to take a good photo is because I have an expensive camera. That's not true. Give an amazing camera to someone who doesn't know how to use it and see for yourself that it's not all about equipment.
I bought my first camera four years ago, and I still use it now. I bought it because I wanted a camera and underwater housing package that was reasonably priced and decent enough quality to take good shots in shallow water. Nothing too fancy. The camera itself is an Olympus Pen E-PL5, which is a Micro Four Thirds mirrorless camera. It has a cool flip-out touch screen and is super lightweight and easy to travel with. It came with a 14-42 mm kit lens, which is wide enough for me to snap some decent half and half photos.
The housing I use is pretty basic. It's the Olympus PT-EP10 housing, which comes with a standard flat port, but I also purchased a dome port from Zen Underwater. I've had this camera for 4 years and only had to replace the o-ring once. Now I'm spending more and more time in the water shooting, I'd really love to upgrade this setup!
The rest of my equipment is Nikon. Lots of people make a fuss about what brand you use, but I really don't think it matters. I chose Nikon because the person who inspired me to buy a camera was a Nikon user, and helped me choose my equipment. If he had been a Canon user, I would be a Canon user as well.
I have two camera bodies - a full frame D750 and a D7200 crop frame. Why do I need two cameras? Because cameras fail. If you're serious about being a professional photographer, you need a back-up camera. Also, the crop frame helps me get even closer when I'm shooting surfers from a distance.
I have four lenses. A Nikkor 50 mm f/1.8 prime lens, which is my most recent purchase and is the widest aperture lens I have. A Nikkor 24-120 mm kit lens, which came with the D750 and is a decent all-rounder if you need something versatile. I have a Nikkor 16-35 mm f/4 as my wide angle, which is my favourite lens for landscapes and if I had a housing, I'd take this lens underwater as well. Then I have a Nikkor 80-400 mm telephoto lens, which is the monster on the right. The shots I can get of surfers from a distance with this lens are incomprehensibly sharp. I also get a lot of compliments from strangers when I'm walking round with this bad boy.
And that's it. I have a Pelican case that I take as carry-on when I travel and I just about manage to fit everything in it if I pack it in a very specific way! It fits every airline dimension restrictions but if I'm honest, it weighs about 15kg when full. Somehow I've gotten away with it every time...