Maybe have several smaller round tables of buffets, that all have the same selection of food on, rather than one massive table, where people insinctively form a queue at.
Also a smaller selection of food, rather than dozens of different items, so people don't feel they've missed out on something that's run out, because there's lots of everything that's there.
And make just about all of it vegetarian, with a couple of things that are vegan. Too many times a buffet will be dominated by sausage rolls, pork pie, sausages, ham sandwiches, quiche lorraine, which are effectively much the same food.
Have lots of things that most people like, that happen to be vegetarian, like onion bhajis, good bread, cheese, pickles, hoummous, carrots, falafels etc and then you don't have to worry about running out of vegetarian food because a non vegetarian has dared to pick up something not made from processed pork.