Prior to the film's beginning, make sure to add a column in the contract for both cast and crew that discusses food: what they like, don't like, allergies, the works.
Be sure to stress this part of the contract when they go to sign. If they don't let you know of their dietary requirements, how will you know?
Once all of the contracts are gathered, compile everything into a list that informs you what the majority of people like to eat, can eat, would prefer not to eat, as well as which foods cause allergic reactions.
Analyze the list to come up with the consensus opinion on food. On a film shoot, you may need to provide food for 1 to 3 months, if not more, meaning everyone should be able to have their desires met.
Regardless of the majority, or main course, always be sure to have some sort of salad bar setup or something for those who cannot eat the main dish. If 97 out of 100 people can eat fish, it isn't worth canceling a fish order to appease the remaining three workers.
Order a dish that the majority can eat, but take individual orders as well. Not everyone needs to eat the same thing.
Go the extra mile. These are your workers and they should be treated fairly. Coffee and tea dispensers should be on the set at all times, as well as some form of a salad bar and perhaps even a dessert table.