One of the things that makes zombie survival sim DayZ so difficult is that players start the game without a map. Even later on, getting hold of one can be tough. Without a map, you can't see where you are, and if you don't know where you are, you have trouble finding other survivors.
Sure, you can get around this by just downloading a map, but that's hardly as authentic an experience as buying a large, $15, real-world map to have sitting next to you, is it?
These were first printed up last year, but given DayZ's popularity - and its lack of map - ArmA II developers Bohemia Interactive have decided to start selling the things.
Other recommendations for a more authentic experience: drink a can of pepsi every hour, shoot the first person who knocks on your front door and don't go climbing ladders with your pistol drawn. Even in the real world.