Boromir didn't actually travel in uniform though did he? And would not have sought battle journeying alone so he is unlikely to have wanted full armour. Of course in the book he has no armour and is dressed for riding. If he had armour I guess he would have discarded it when he lost his horse. I doubt he would have taken precious and ceremonial armour on such a journey, or anything else that woud draw attention to a lone traveller. As a backpacker, it is a principle that holds true now - don't take anything you can't bear to lose or that will make you a conspicuous and a target for thieves.....
