things like booking the room, requesting additional equipment, telling the candidates what to bring and what they will be expected to do, briefing the panel, ordering coffee, ensuring that there is water and glasses. Arranging a waiting area for the candidates, telling reception who is coming and what to do with them or arranging a greeter. Booking the panel and getting their manager's permission if needed. CHECKING that it will all happen. Arranging for it all to be cleared away afterwards.
In real life its often these "duh" bits that fall down.