There is a thread on here that deals with the quantities for vending that takes into consideration the number of vendors, the number of people who will not eat ect ect. We used it for the first time we vended and ended up purchasing way more then we needed due to the organizer inflating numbers.
We bought most of our stuff at Sam's so we were able to take back alot of the purchase so that helped. However we cooked alot of PP prior to the event and it carried us through without having to cook the rest. We were able to put that into the freezer and was able to cook and sell it for catering events later in the summer.
Like somebody said above better to run out than have a bunch left over. You might want to add something to your menu that you could cook quick if you find yourself with several hours left to vend and no food.
KCBS CBJ 9831
Large Spicewine, Backwoods Smoker (Party), WSM, Oklahoma Joe's Offset, Wood Fired Oven