With Bungie you never know if it's actually a key to a Easter egg.
The Stranger hands it to you. This could be Bungie's way of saying this is important for other things.
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Oh the things I have lost before the vault expansion. At Lease I kept shadowprice, the swarm, zombie apocalypse, epitaph, proxima centauri, tdyk, tdyd, unfriendly giant, final boss, many shotguns. Lost some better looking armor though...