This page has all of the items in the DLC that were released through DLCs. The Suitcase and the Padlock are from the first DLC, released on 9/13/15. The Re-atomized release of the game includes all of the previous DLC content.
Suitcase[]
Main article: Suitcase
The Suitcase in the shelter.
The Suitcase can be used to bring 3 extra items on an expedition. Also contains supplies In scavenge mode on Little Boy and Fat Man difficulties as seen in some events in Journal entries. It is a good item, but weighs as much as Mary Jane or three small items, so in Fat Man difficulty it isn't very useful. It won't always be brought back from an expedition. It is probably not worth going out of your way to get it in Tsar Bomba difficulty, instead the player should get more Soup Cans and/or Water Bottles. There are also events where a suitcase appears at the door with either a chance of getting a character sick, having nothing inside or giving the player an item.
The suitcase in the DLC countdown (7) post.
Padlock[]
The Padlock in the shelter.
The Padlock in scavenging.
Main article: Padlock
The Padlock can be used to lock the fallout shelter to keep raiders out (but may be lost) and be taken as an expedition item. If the Padlock is brought on an expedition, the player will receive 2 Water Bottles after the expedition. In general, it is very useful, and only weighs one inventory slot in scavenging. The player can trade it away in trading events. It cannot be repaired with the Boy Scout Handbook.
Hats[]
Hats were added in the It's not rocket science DLC. They are added by completing challenges. Good hats use good items.