If it’s a paid in advance 1 per person cap on 400 deal…you or the organizers will need to implement a ticket/voucher etc. system to keep track of that.
Also…when you cater to a 1 per person anything you have to be prepared with a quick answer or a fast plan when x percentage of people start to tell you that they are really hungry and would like to purchase an additional hot dog. That will especially apply when catering to college students. Talk to the organizers about that before the event. That can slow things up…for sure.