I watching football news this morning and Brazil (u15) lose a game on default to Peru because the coach made 4 subs rather than 3. Now the first thing come to my mind is what the hell is the 4th official for. I mean he eh really have that much to do.
Make sure the coach stay in his technical area. which they does enjoy doing.
Hold up the extra time board or fingers if no board available
Tell the physio & doctor the Ref say its ok to go on
Control the substitutes including recording it against the game sheet