A straw hat with real grass growing on it.
It's made of two layers with some soil and grass seeds pressed between them. The bottom layer is water-tight. You water it to get the seed started a week before you plan to wear it. Thereafter you water it once per day.
I'm not really sure. This idea came to me in a dream:) It seems suitable for beach parties or burning man type of venues.
If you are going to be in direct sunlight for a while and don't mind looking silly, the grass actually provides better protection from the heat.