If you can I'd take a small hat and a buff, just in case you get caught in some really grim weather. The buff can then mask the bottom of your face whilst the hat can keep your head warm. That said I'm reasonably
sure a buff alone would do as a hat but, if you don't know already, the kit checks for the fellsman are taken uber seriously, to the point of checking fell shoe studds and not accepting space blankets and insisting on survival bags