Here is my gear list with my rationale on how and why I use each piece.
Canon EF 24-70mm f/2.8L USM - This is my most used lens at weddings. I favor zooms over primes primarily so that I can change the angle of view. I can stand back and isolate the bride at 70mm, them step closer and switch to 24mm to get the bride and her bridesmaids behind her. All in a couple of seconds. I haven't "upgraded" to the mark II because I'm happy with the sharpness, I like the design and build of the mark I, and also the filter size. Plus if like to have IS for video when I upgrade. I use this for macro shots as I don't find the need for 1:1 at weddings.
Canon EF 70-200mm f/2.8L IS II USM - used during ceremony, bride/groom portraits and reception. Mounted on my second body. Decent lens.
Canon EF 24 f/1.4L II - Selective focus AND wide angle of view! My favorite lens. I'll use this for low light situations, like a really dark church where they don't allow flash. I'll shoot at f/1.4 but I'll back up to get enough depth of field.
Canon EF 40mm f/2.8 STM - backup to the 24-70mm. Sometimes used at the reception when I want to keep a low profile.
Sigma 85mm f/1.4 EX DG HSM - Like the 24mm, used for low light situations. I might switch out the 70-200m if the church or reception venue is small.
Canon EF 200mm f/2.8L II USM - a backup to the 70-200mm. It doesn't have IS, but it's sharper, less conspicuous and focuses faster than its big zoom brother.
Canon EOS 5D Mark III x 2 - I used two 5Ds before this. I upgraded to get two card slots, video and better outer AF points. All else is gravy. I could lived without the faster FPS, higher resolution LCD and even without AF tuning. I would like DPAF and touch screen for video, and a highlight metering option like Nikon had started including. Cleaner shadows perhaps, but not much else.
Canon Speedlite 600EX-RT x 3 - I like the built in RF communication. I use one flash on each camera (master/fill) and the other in hand (slave/key), usually at a ratio of 1:2. I have a Demb Flip-it! on each. I always try to increase ISO to expose the background through ambient, so I will almost never drain the batteries of my flashes.
Yongnuo YN 600EX RT - a cheap backup.
Yongnuo YN-E3-RT x 2 - Used at receptions on each camera when I don't need fill. I'll stick two flashes on a light stand and bounce light off the ceiling.
I wear a Cotton Carrier which helps alleviate the weight of the gear. I'm considering adding a belt or just pouches with belt loops to hold a lens or flash on my person.
I sometimes bring my 70D and the 10-18mm to get really wide shots of places, but only when I'm shooting with my partner.