Hmmm, it depends on how you shoot and how long you're planning to be there. For example, I took approximately 1100 shots at the last wedding I shot. However, that was from some shots of the reception hall before everything started, as guests were coming in to the ceremony we did quick portraits, and then did table portraits as well as the usual shots and candids. Plus I have a tendency to shoot way more than I need just so that I can be sure that at least one or two of the shots come out the way I want
But like I said, a lot depends on your shooting habits. If you don't shoot a lot in burst mode, 400 might be ok.
Are you doing formal group shots as well? Because that will easily start eating into the number of pictures since you'll want to take a few shots to try to make sure that nobody is blinking (see the blog post on
group shots). So that could easily take 50+ of your shots.
So I'd really probably say get another card or two, just to make sure. At least memory is one of the cheaper things you're looking for
