ok, now, don't laugh... remember when you were a kid, and you took newspaper and folded it into a pointed old fashioned admirals hat...

Well, in a raging downpour, when I gave my rain shell to my kid... I donned a trash bag, and for my hat, I folded my Tyvek trail map into a hat. It actually worked reasonably well when it was just a downpour, but, when we got into some wind I needed to break out the duct tape. I'm glad we didn't get a photo of that, my son would never let me live that down.

Maybe you can carry a Tyvek bandana?