After talking to Crow (Satellite) go to the B.A.D. Area (specifically the areas where you fought the Dark Signers). Then defeat all Dark Signer Shadows in both Standard and Turbo Duels at the respective locations. (Your Life Points are not reset between each duel) Then go back and speak to Crow to unlock the pack. Also, if Crow is your current tag partner he will not be where you first saw him. You must switch to another tag partner.
After talking to Kalin (B.A.D. Area/Enforcers HQ) go to the top floor and defeat all Enforcer Shadows. (Your Life Points are not reset between each duel)
After talking to MC (New Domino City/Stadium Lobby) go to the Stadium and defeat all Signer Shadows. (Your Life Points are not reset between each duel)