I broke down and bought one of these traditional conical hats for $5. Not sure where I am going to wear it, and it was a pain hauling it home on the airplane.

Note the young woman wearing a mask. I always thought that these masks were to protect the wearer from germs or smog. However, both our guides told us that the primary reason is to protect the wearer from the sun. Pale skin is much admired by Vietnamese women.