Hi, I recently shot a "wedding" which was actually a renewing of the vows for the Scottish relatives after the couple were really married in Aus.
That aside, the shoot only lasted a few hours from 10 am till 5pm and managed to take over 500 shots.
I would agree with all of the above
Kit-
Ensure you have charged your battery's the night before
Enough memory cards how many shots per card?
I had 4 x 4gb used 2 shooting in raw
Extra body - just in case the other fails- plus you could mount another lens and use for wide angle shots.
Flash - sb800 plus an invaluable lumniquest quick bounce- which helped fill the shots in doors with bounced light as opposed to direct flash.
the usual accessories - blower and lens cloth
Previously I met up with the couple and we drew up a plan or list of shots which they required.
Speak to the minister to ensure you are allowed to take some shots.
Check the location if you can,
Remember you are documenting their day, so there is quite a lot of reportage and scene setting shots.
Hope this helps, besides that have some fun !
cheers
R