Back in the day, only kings could eat like kings, and they were supported by villages full of peasants allowing them to eat like kings. Nowadays, more of us eat like kings than the world can really support, and it is by the grace of petroleum and third-world nations that we are able to do this. So the first thing, I think, would be to stop eating like kings and start eating more like peasants. Flying in pineapple to Canada and feeding grain to cattle are not, ultimately, sustainable. The trick is getting people who are used to, and love, eating like kings, to give it up. That’s where etiquette would probably come in.
Ditto transportation. Having the work equivalent of hundreds of peasants (oil) dragging us around from place to place is not that sustainable either. Cities need to be more pedestrian/bicycle friendly, and we need to eat more locally.
Everybody wants to be the King, or at least have a lifestyle that exceeds that of actual medieval kings. Supporting kings is, however, taxing. ;)