These passwords are entered at the Extras screen under Password after beating the game once on any difficulty. The items will be made available upon loading your save game or starting a new game (in which case you will gain access to them when you meet up with Metal Gear Mk. II; iPod songs are immediately available.)
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george --> Unlocks "Gekko" iPod Song

thomas --> Unlocks "Desperate Chase" iPod Song

theodore --> Unlocks "Midnight Shadow" iPod Song

abraham --> Unlocks "Mobs Alive" iPod Song

mekakorkkk --> Unlock Mk. 23 handgun (SOCOM from MGS1)

mnsoymsyhn --> Unlocks "Mosin Nagant"

deskyhstyl --> Unlocks the Desert Eagle Long Barrel

1aytmmymhk --> Unlocks 1911 Pistol

jmsotsynrn --> Type 17 Pistol

aottrykmyn --> Altair Costume

dntkkhktmm --> Drebin Facecamo

mgo2play --> Unlocks "Subsistence Action" iPod Song

tshsniammr --> Unlocks Thor .45-70

pkhhnwhsjt --> Unlocks Patriot

skynytktjp --> Unlocks Scanning Plug S