COGS

Where would you start looking for answers?  Or is my calculations off...
Weekly Beginning Inventory 7,000
Purchases              +   2,000
Ending Inventory  -   5000
Cost Of Goods = $4000.
So far so good...
Food Sales(pretax) $10,000
So food cost = 40%, right?
My problem is that every menu item is priced at or below 30%(averages about 27%).
27% food cost on $10000, is $2700, not $4000 as in my COGS.  So where did the $1300 go? 
Ideas:
* waste- That's ALOT of waste, I'm sure it's part of it, but not that much.  My waste sheets weigh in around $100/week
* theft- self explanatory, but $1300 worth of food is alot to steal.
* employee benefits- free meals.  But the are included in the sales already(just received as "discounts")
* Mis-categorized items- Is it customary to include toilet paper, cleaning supplies etc. in food cost?
My gut is telling me that's its a combination of all of the above, but any insight and opinions are welcome..
 
Todd