Q:

How do I unlock all of the promotional content?

I read There are four promotional unlocks in Borderlands 2. What are they? and was wondering if there are (legitimate) ways otherwise to unlock this exclusive content.
I've also been thinking about how the players that I've seen speed-running this game all use a sniper rifle that seems to be rewarded by the Premiere Club promotion. So, being able to unlock that content would help speed-runners who didn't pre-order the game.
I suppose that the answer to this question should include (mention of) SHiFT codes.

A:

From There are four promotional unlocks in Borderlands 2. What are they?:

The Creature Dome from Gamestop.
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. 
A special grenade mod(not sure what the source of this is)
Special character skins(Collectors Edition unlock)

The Creature Slaughterdome has since been made available for purchase.  
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."
Contraband Sky Rocket
There is a Collector's Edition Pack that can be bought.

