"What is the significance of the food that is eaten at ISKCON kīrtanas?"
The significance of our food—not exactly vegetarian or nonvegetarian. Don't mistake. We simply take what is offered to Kṛṣṇa. That's all. So Kṛṣṇa can be offered anything? No. Just like if some guest comes to your house you ask, "How can I serve you? What foodstuff you'll like to eat?" He says: "I like this." "All right."
Similarly, we are order-carrier of Kṛṣṇa. We ask Kṛṣṇa, "What do You want to eat?" And Kṛṣṇa says in the Bhagavad-gītā that "Give me vegetable, fruits, liquids. I shall be very much pleased." So we offer Kṛṣṇa fruits, grains, milk, and their preparation. They're very nice. If you come here and eat with us, you'll forget meat-eating. You see? It is so nice.
So our proposition is not that vegetarian/nonvegetarian. Vegetarian or nonvegetarian, it is not very important thing. Everyone is eating some living entity. Vegetable has got also life. It does not mean that one man is eating meat; therefore he is killing. But even vegetarians, they are also killing. But our process is . . . we . . . killing is not very important or nonimportant for us. If Kṛṣṇa says, "Kill," we can kill. If Kṛṣṇa says: "Don't kill," we don't kill.
Because we are simply order-carrier. Just like Arjuna. Arjuna was posing himself by his family relationship that he's very perfect, nonviolent gentleman. But Kṛṣṇa induced him to fight, to kill the other party. So for us, killing or nonkilling is not very important thing because everyone is killing, knowingly or unknowingly. So our point is we take foodstuff offered to Kṛṣṇa, and whatever Kṛṣṇa eats, that is our foodstuff. We distribute that thing.