A wireless microphone is shipped with every GoPro package. We recommend placing the mic in the groom's pocket or right near the groom/officiant during the ceremony. To get the best sound of your toasts, just place the microphone right at the table where they are offering the toasts.
When we get your GoPro footage back in the office, our editors will sync the recordings on the microphone with the GoPro footage so it will sound awesome when you see it in your storyboard!
Here are printable instructions for the microphone.