From http://gaming.stackexchange.com/questions/85115/there-are-four-promotional-unlocks-in-borderlands-2-what-are-they:
> 1. The Creature Dome from Gamestop.
> 2. Premiere Club(all preorders) - I presume for the purposes of this file, it's just the Gearbox Guns and Vault Hunter relic and not the
> free character DLC and golden key. 
> 3. A special grenade mod(not sure what the source of this is)
> 4. Special character skins(Collectors Edition unlock)

1. The Creature Slaughterdome has since been made available for purchase.  
2. Mechromancer Pack: "In addition to this new class, this pack also includes bonus items which were included in the Borderlands 2 Premiere Club Pack, including the Gearbox Gold Gun Pack, a Golden Key, which unlocks rare items in the mysterious Sanctuary Loot Chest, and the Vault Hunter’s Relic, which boosts your gear-hunting fortunes."
3. [Contraband Sky Rocket](http://borderlands.wikia.com/wiki/Contraband_Sky_Rocket)
4. There is a Collector's Edition Pack that can be bought.