Near Bear Room Quest room you can see a chest (near a switch) that contains a backpack with a Present and some other stuff. Take it. You can keep the backpack and you need to keep the Present for later - The rest is totally useless. Now go to Seymour (here) and say box. He will trade the Present for a Legion Helmet.
Notes: A Rookguardian planning to stay may prefer to keep the present, as it is lighter, or maybe an item for collectors, since you can only get one Present on Rookgaard. Also, the value of Legion Helmets in mainland has slightly risen because they are not dropped by Rotworms anymore but still needed for an outfit quest.