Shroom,
When I was in charge of special events planning at my last account, we always broke each event out like this:
Food
Labor
Rentals
Other
Specifically, once the menu was written the order guide was scribed and the the neccesary rentals were lined up. The rentals will dictate how many tables, etc, therefore staffing follows. The 'other' column was usually a large enough category that somebody was designated to take care of the 'loose ends' (of which there are sooooo many). Like where exactly does the porta-potty go? Do we need to buy ice? If so, how much and where do we get it? Signs... tickets... cash-handling...
I would examine one aspect at a time and start making a chart of Item, Who is Responsible & Timeline (status, completion)
Help ya'? Hope so. And just remember, it all seems to fall apart an hour before the event... and then come hurdling back together 10 minutes before the first guest arrives.