At least make sure you have a backup for everything.
I've only done this once so this is not an "advise" but sharing my experience.
I pretty much took everything I owned but at the end of the day, these are equipment I actually used.
A body with 70-200 f/2.8, potato masher flash
Another body with 24-70 f/2.8, flash on a bracket
105 f/2.8 macro lens
Spare for every stupid thing
I carried two setup at all times with me. Rest of the gear was in groom's room. I had an assistant to do "chores" when I needed. She (my girlfriend) was probably the most useful "equipment" I had of the day. Lining up guests, finding someone, fetching what I need, I couldn't have done all this by myself.
Did I tell you this was my first time? Did I tell you to have backup for everything? Well... the ONLY thing I didn't have a spare of was a cord that goes from flash to camera body because the flash was on a bracket. This was purchased new and tested for few weeks. Guess what failed.... an hour before the "show" starts.... I had to troubleshoot it quickly and remove the bracket, smile, and get ready.
I did most of the shoot with digital gears. I had one film camera for few shots. I may get a flack for saying this on APUG, but be very careful about selection of your media... this is THE day for the couple, family, and all the guests. Not a day for our hobby.
For an interesting perspective on weddings, equipment, and other things check out http://www.aljacobs.com/
If I decided to shoot weddings again, I would probably go back to the equipment I used to use:
Mamiya TLRs - C330 main body, C220 backup;
65mm, 80mm and 135mm lenses
Metz 60CT2 and Metz 60CT1 flashes
Gossen hand meter
Portra film - 220 and 120 - mostly ISO 160
Pro lab proofs - 5x5
I never said quality of the product was the reason I chose the other media. I have significant investment in film and film equipment here, and I do most of my "artistic" work for myself on film. My point was to think of the couple first - not the hobby. Being the first time wedding shooter that I was, the ability to view the result - to at least make sure half way decent image was recorded was high on my mind. Great tonality and artistic expression was far down the priority. So once the official wedding started, I used the "instant" method. During the low time before the "show", I used my film to shoot what I'd like to keep and enjoy.
The point I was making was, it is a serious business to be a wedding photographer - paid or otherwise. (I was a volunteer photog for a couple who had very limited $$)
With either method you just need to know exactly what your camera and film/sensor is going to do to have the confidence that what you are doing is right. Once you have that, everything will be fine.... even the digital user will not need to look at the back of the camera after every (or any) shot!