I have buddies that came from the days when MF cameras were the cameras of choice for Weddings, it is fun to here them talk of being sent out with two rolls of 120 and being told not to shoot it all, I'm not suggesting that.

Typically weddings are hurry up and wait affairs. Just load during the waits and have enough backs to get through each hurry up.

If you know basically what shots you really want in each hurry up and when they will be, you can plan for that plus a bit extra.