I usually wear Crocs Santa Cruz loafers.

They give you all the comfort of Crocs material, but they look like normal shoes. The best part is that you can fold the back down and they essentially become clogs temporarily, which is great for airport checkpoints and such.

For more casual situations I am usually wearing a pair of Scutes. Those are the most comfortable shoe from Crocs (by far, IMHO). But not quite up to flying in first or business class. Maybe steerage.