Seconds Cub Scouts frequently have eyes which are larger then their stomachs. Tell them that they can come for seconds if there is enough. Announce when seconds are served. Friendly Serving efficiently does not imply being unfriendly. Relax, don't squeeze the eating time but announce new times for the program.
People like to know what is going on.
Have things ready to clean up a spilled plate. I think not. What is necessary is that we try get something for everybody. Make sure the servers get to eat too.