Add the following to the list of things a customer can consists of

Allergy

Can be any one ingredient or “none”. When the Yard creates a Customer, they should secretly random determine a possible Allergy for a Customer, with equal weight given to all ingredients and to “none”. A Customer whose allergy is not none can never select an dish which contains an ingredient which matches their allergy—those dishes are always excluded from any selections the customer might make (including upgrading to a signature dish)

in the Sale atomic action after “The Yard selects a random item on that Truck’s Menu to be the Active Customer’s Choice” add ” (if no items are available due to Allergies or other restrictions to the Customer’s selection, skip to the “They leave the plaza” step)