When I ran a series of workshop in higher education we had over 300 delegates at 15 workshops in a 12 month period. At every event the catering was 100% veggie. No complaints, very little wasted.
And one other minor point, fish isn't veggie! It's got a face, it breathes, it's meat. Although the 'fish sticks' prepared below by Epicurious couldn't actually be identified by any of the meat eaters at the event, other than it smells fishy. Of course it may have been that they were just fried with the king prawns (big insect like things, they both faces and feet hence NOT VEGGIE).