It is vitally important to have a large variety of Photography kit for Weddings. This never ending list you will forever be adding to as there will always be something that you feel will make life a lot easier.
However for me these are the basic "I cannot photograph a Wedding without" list.
I am sure every Wedding Photographer will have some slight variations of the below as its totally subjective.
I personally Photograph using a Canon Eos 5dmk11 with a back up DSLR of a Canon Eos 70d.
I find the full frame on the 5d allows me to shoot those extreme wide angle shots that are very popular today.
The 70d is a fantastic back up - and sometimes I actually prefer its body for the screen options. My only advice regarding DSLR's is buy the best you can afford and that feels good in your hands.
Weddings need a variety of Lens options as no two Weddings are the same. The weather in the UK changes quickly, changing from inside to outdoors in a few seconds and of course needing the capabilities of being able to do wide angle along with stealing that intimate moment from a distance.
For me the two must have Lens are:
24mm - 70mm F2.8
This Lens allows you to take all those wide angle to portrait photos - the F2.8 will still struggle in low light, but overall a fantastic multipurpose lens
70mm - 200mm F2.8
This Lens allows you to be unobtrusive and capture moments the guests and Happy Couple didn't even know happened. Often it is better to be further away as then the moments are real and natural (rather than the standard pose when guests see a camera pointed their way),
Other Lens options that are super handy:
Alway buy the fastest you can afford
Always buy the fastest lens you can afford
As shown in the photograph I have a Canon Speedlight - however I also use Elinchrom Flash systems. Unless you want to buy shares in Duracell I highly suggest purchesing a battery power pack to go with whatever flash system you are using. Weddings often need a lot of Flash due to the dynamics of the day. Nothing nicer than seeing that lovely balance of fill in flash / bounce on the couples faces.
This list literally is endless but there are a few obvious additions for Wedding photography.
Batteries - lots
Whether its for the cameras / flashes / microphones - make sure you have enough batteries to last you a week. The last thing you want is your spare batteries to turn out to be flat / dead - so you need spare spares, and some more spares.
Memory Cards - lots
As with batteries you can never have too many memory cards. I'm personally a fan of slightly smaller cards that I change throughout the day - the reason being that IF the unlikely yet horrendous situation happens of a card becoming corrupt, and you loose some of the images whilst you send the card to get recovered - you still have the rest of the Wedding on the other cards to be working on.
Holster mounting - for each camera
This will make your life so much easier. The industry known standard is a Spider Holster. However I actually use a Capture Pro. The reason being that its so versitile. Attach to a bag, a belt, a tripod - means you can use it however works for you.
A good quality Tripod will see you the rest of your career, dont go putting your expensive gear on something cheap!