Several items not related to equipment per sei:
Scope out the place where the wedding will take place and get to know it intimately if you can. Practice where you will be at for the shots. Remember, the wedding is about THEM not you.
One of the most important items is to find out WHO you are going to be answering too. The bride, Groom, mother of the bride, mother in law..who?
Ask about who gets photos and who doesn't. One item I have run into is that guests ALWAYS ask for copies. Ask the bride and groom if this is OK with them.
Consult with them about the style and manner of photos.
Find out if they want photos of the rehearsal (if any), reception, bride arriving, couple departing, etc.
You don't want to become a distraction. Try to set up a spot behind the alter if possible to get shots of the wedding party coming down the isle.
Practice with the lighting that will be there, try to keep note of the white balance (if digital) or any filters needed (if film).
Find out the colors of the wedding and get appropriate clothing. (rented or not.)
Talk with the minister/priest/rabbi/cleric/ who ever to find out if flashes are allowed. (Many churches and other places wont allow flashes.) If so, get ready to shoot with a higher ISO setting.
Find out about certain cultural issues. (i.e. if photographing certain people, items, parts of the ceremony etc.)
Carry extra batteries, memory cards, etc. If you get a digital SLR, shoot RAW as much as possible. Then convert to jpeg. (Trust me on this one).
WATCH it with any portable lighting. (Cords are great liability issues, and can be very tempting to a 4 year old.)
DO NOT SHOOT UNDER COLORED TARPS!!!!!! When I worked in a photo lab, two guys showed up with rolls of film from a wedding. They had shot the majority of it under a green tarp. We wound up converting many of the photos to B&W as a result, and it saved the photos!
Ask about B&W by the way, and look into posed shots of the following:
Bride looking in the mirror, groom horsing around with his 'buds'. Family shots, etc.
Go here:
http://books.google.com/books?q=wedding+photography+books&ots=201TjpNRs4&sa=X&oi=print&ct=title
Also go to the local book store and read. Then go to the local camera store and ask questions!!! Lots of questions. Yes several will try to dissuade you from doing, but DO NOT LISTEN to them. Any guests that try to get you to do certain things, remember you are answerable to the couple, not the guests.
Weddings can be fun. But to reiterate! DO NOT MAKE IT ABOUT YOUR WORK! It is about the couple.
Good luck and have fun.