I just bought a running cap from the north face called the better than naked hat - very light, should dry super fast and looks ok. We'll see how the DWR goes... Brim will definitely block some sun and rain, and is quite flexible so shouldn't deform if I'm halfway careful.
To answer your other questions Tanner, I'll be wearing a merino buff and will see how I feel on the ground and may buy a merino beanie from 66* North (part practical, part souvenir) on the way through Reykjavik.
I'm going mid July for 3 weeks, hiking from Asbyrgi to Myvatn, Fjallabak trails,Laugavegur, up that volcano and some day hikes around skaftafell, with some bus journeys in the middle. Since I'm not camping in the highlands I hope to avoid the worst wind/storms... I'm sure my cuben duomid would survive a lot, I'm mainly concerned about pitching it in those conditions... My hardshell is a kind of midweight affair from Patagonia, with substantial enough zips, but I'll be mindful of your advice when zipping and unzipping my Houdini...