I'd disagree with Allen's advice about a baseball cap. A wide brimmed hat will protect the top of your ears and if you get serious sunburn there it hurts like hell...... I discovered this many years ago when I had a long hunt in the Zambezi Valley in Mozambique and I ended up with the tops of both ears completely covered in scabs.

Actually, when I look back at it, it wasn't exactly the best hunt I've ever had as a little later I almost died of heatstroke........ but it was a loooong time ago, when I was young and dumb.