On my current game, I'm prepping for a run through Dead Money. Since it's the only DLC I cannot go back to once it's completed, I'm wanting to pick up absolutely everything rare (playing cards, vendor codes, weapons, armour, mods, etc) as I go through. Is there some kind of checklist out there, or do I need to start browsing Youtube to make my own?

The Vault usually has all you'd need in terms of item scavenging in Dead Money.

Wiki aka The Vault is your friend.