We've done some major events in the past: Harleyfest-The 100th Anniversary of HD, US Cellular Tall Ships, & EAA Fly-In. Here are some factors to help increase business.
1. Meet with the events chairperson and request to see the vendor placement. Request a location in the traffic pattern which places you at the beginning of the food vendors. This is where people will immediately see you first before they have an opportunity to walk past everyone else. If you don't like your placement, don't take "no" for an answer. Be persistent in getting your location. This will make or break your success. It only takes once to get burned and it's no fun watching customers buy food from other vendors before they ever get to your cart.
2. You'll want to park your vehicle with extra product as close to your cart as possible.
3. Follow the weather forecast carefully and bring a 10X10 pop-up tent in the event of rain.
4. There's no formula for determining the amount of product. Since you'll be selling after the event, any unsold product can be refrigerated or frozen for future sales. If you over buy, it's not a big deal. Like BR mentioned, if you select a dollar amount as your goal, you'll need that much product. There are no guarantees in this business.
Born in Chicago
Escaped to Wisconsin
Selling Vienna Beef hot dogs & Polish