We use a fountain pop dispenser for our events. Very economical, no cans or bottles to handle-you just throw the cups in the trash. Our distributor gives us a nice discount and we get credit back for all unopened sleeves of cups and untapped canisters. If I remember correctly the pop for our carnival was less than $60. That was for 475 students and their families.
We too are planning a fall festival with food. We have contacted large local businesses to sponser just the dinner and have already received several hundred dollars to offset the cost of food. Many places are happy to give you $25 and every little bit helps. Local unions and politicians (like alderman) often kick in too. Just an idea you might want to try. Our local grocery stores have also donated gift cards with which to purchase food. Last year we spent $300 out of our budget for food and this year we are spending 0, thanks to my husband who is food chairman--I am so proud of him!
Also check prices on items as hot dags etc with the ventors the school lunch program uses with the "big clubs". Our "guy" has met prices before so one- I will "use" him and two- he knew I valued the fact that he would deliver everything I needed versus shopping with two preschoolers! (delivery...priceless!) Also might be worth seeing if the lunch program would be willing to purchase your unused "left overs" and offer them as a special menu item to the staff, that's a big one but worth asking.
As far as quanities, I have a cookbook with a chart that was written by the FDA. No clue how old it is but has been my best friend!!
Thnkas for the great ideas. We own a popcorn machine so we will already be doing that. We aren't too concerned about profit, we do this for fun. Maybe I will think twice about the nachos. I appreciate your help, I hadn't even thought about popcorn bags yet.