Yes, I bring 3 camera bodies to a wedding as you never know what might happen. I also use various lenses and bring at least 5 or 6 to a job. I also have spares of everything else that I use as I prefer to be prepared and concentrate on the photos rather than be concerned about my equipment.
I use cameras that record to dual media slots, this means that every photo that is taken is recorded to 2 separate cards simultaneously. This way I automatically have a backup of a photo as soon as it is taken thus reducing the possibility of image loss if a card should fail.