I started doing vendor jobs before I ever did catering. My formula for figuring how many I will feed works very well for me, in my area, but every place is different. I take the number of people estimated to attened and figure 25% of the total wont eat at all. Then take the number of people left and devide it by the number of vendors selling food ( don't include the ones that just do popcorn, icecream, smoothies, etc.) That will give me a realy close estimate on how many people I will feed. Only problem with this method is if nobody knows aprox. how many people are going to attend. (ie: 2000 people -25% = 1500 devided by 4 (assuming there are 4 other vendors) = 375 people that will probably eat at your booth.)
Of course there are alot of other factors that could make the numbers go up or down; weather, location, day of the week, alot of older or younger people, etc. I have found that if I am the only BBQ vendor I tend to do more business than the other food vendors so I would adjust up for that. If your the main food vendor and all the others are the snack food type, then I would plan on almost the full 1500 people.
I always priced my food in even dollar amounts so I didn't have to mess with loose change, and I always had a "combo meal" on the menu ( even if you don't save money by getting the combo meal - people just like the ease of ordering it)
And make sure you are charging the right amount $$$$. You can always get better prices at events like that.
Make sure you have 3 wash buckets and a hand wash area (you never know when the health dept. will show up.)
Bring some folding chairs so you have a place to sit and I hope you have some people helping you so everyone gets a break. Standing all day in a food booth will wear you out fast. Bring extra ice and $1 bills you will need them.
I almost like doing the vendor booths better than catering beacuse I know what to expect, and I am not dealing with just one person who is paying the bill. I got alot of catering jobs from doing my vendor booths too.
Good luck, and remember to have fun !
Some people are like Slinkys, they are good for nothing but can still bring a smile to your face when you push them down the stairs.
Down to one lonely ol' Bandera.