I can help the ceremony, breakfast, speeches, grand entrance, etc. As many weddings where we do the ceremony music and afternoon breakfast music and speeches, there doesn't seem to be anyone in charge!
Sometimes its the best man, who is usually too nervous to say anything, or the wedding coordinator might not know what to say either.
So I usually take it upon myself to help out in these circumstances, and jump in last minute to get everyone to stand and cheer when you come into the room for the breakfast.
Or help out when its time for the speeches, and introduce who is next to give theirs. Guests also need direction from time to time, and information as to what is happening. Plus its good for me during this time to introduce myself to the guests and maybe find out what songs they would like later on.
But it would be much better if a particular person knew they were responsible for these things before the big day, so for a minimal extra charge, I can look after it if you would like.