I am completely shocked by the poster who said their entire school has to eat silently every day at lunch. Complete silence?!? Isn't lunch supposed to be a social "break" time? These are children we're talking about, not soldiers.
In my opinion lunch is a time to decompress, visit with friends, enjoy each other's conversation. Does your family eat dinner in silence?
We eat in our classrooms, which I love because then there's not the chaos of most cafeterias. My kids sit in their groups and talk quietly while they eat. My rule is they have to talk with kids at their tables and stay seated while they eat, basically it's the same expectations as family dinner. If they are getting to loud or getting out of seats a lot, I count them to three. If they reach three they lose their Friday Friend privilige, which is to sit with other friends on Friday instead of at their own seat. If it happens again in the the week they lose the movie (I let them watch a movie at lunch on Friday).