Well, first of all, they had communion(aka Eucharist) during the event. During Communion, wine, and bread are consumed. Since it was Passover, a Jewish holiday, they most likely had unleavened bread, meaning it has no yeast in it. A group of Italian archaeologists, led by Urciuoli and Berogno, claim it is very likely they ate a mint-like herb, a dish of beans, and olives. Fish is also likely since this was an extremely common food at the time.