Is this a vending gig where you set up and people buy sandwiches from you?
How many other vendors? How many people attended the event last year? Who cooked last year? Why is the old vendor not coming back? If this is a first year event it is a gamble. Organizer's expectations are usually not met.
How many hours does the event last? Is the event being held during normal meal times? Is this a one day event? Is this a charity that you would like to support?
These questions need to be answered in order to figure out how many people that you are going to feed. Do you have a place to sell any meat that might be left over?
Burgers and hot dogs cook in minutes from frozen product. Pulled pork is labor intensive in comparison and takes a long time to cook.
You can approach this 2 ways---#1 make pulled pork for 300 sandwiches and 300 buns and close if you sell out.
or #2 -cook enough pulled pork for 750 people and get 750 buns and take home leftovers instead of money--or maybe get lucky and go home with lotta money.
I would do more research about the event and increase your odds of making money
All good advice here - Pulled Pork is the way to go. Low cost, high margin, will hold well, and left overs are freezeable for future use. Based on the info you have to date, 300 would be a good number to plan for, if you have a 5 - 6 hour selling window.
300 would be something like 135 lbs of butt ($210), 25 dozen buns ($50), Sauce ($10), sternos ($8), paper boats ($4), Napkins ($5), plastic forks (Somebody will ask for them $2). Don't forget to include the cost of any workers, permits or vendor fees in your overall costs.
So before you get there, you have $289 spent, plus any fees, insurance, gasoline, etc.
300 sandwiches @ $5 each = $1500. Figure all the additional costs, and see what you might make. Good luck!