I shoot with two 5D bodies, one attached with 24-70 L and the other attached with 70-200 F2.8 IS L. When needed for the church shots I have a 580 EX II on the one body and a 430 EX on the other body. I do find it difficult to move around with the flash on the second body hanging from my shoulder but it works good for when I need to quickly flip between the bodies for the longer or shorter lens. Do any of you that carry more than one camera body use one flash and just put it on the body that you need or do you also have a flash one each camera body?
What is your method of carrying the two cameras? I have the one I'm using around my shoulder and the other hanging over my left shoulder.
Compact flash cards in my shirt pocket and spare batteries and backup lenses in my backpack which I put in the church out of the way of guests.