It appears that this achievement is somewhat glitched in a positive way according to DaMikeSC , so when you place one of the collectibles the achievement will unlock, despite this, below are instructions of where to place the collectibles in the sleeping quarters. Along with the locations of which they appear in chronological order.
Placement of the CollectiblesMask can be placed on the coat hanger.
Skull is placed on the shelf on the left side of the room.
Toy can be placed on the right bunk bed.
Crystal can be placed on the desk on the right side of the room.
If you are unsure on where to find the collectibles, read this below.
Where to find the CollectiblesFor James's mask there are
two possible scenarios of obtaining it which is explained in the spoiler tags.
James Mask Scenario 1
The
Crystal and
Toy collectibles can be found inside the cave that you go to, you can get these while you're looking for a way to cross the stream of water. The
Crystal will be on the left side of the cave near the water and the
Toy is on the right side of the cave next to where AJ is standing.
James Mask Scenario 2 *** Spoiler - click to reveal ***Lily Death (James Alive)
If you chose this option, the mask is obtained through use of certain dialog when speaking with James inside the cave after you’ve crossed the small stream. You will want to choose…
“The Way You Think Is Dangerous”
Once you’ve done that regardless of what you choose for AJ the mask will be picked up from the floor.
The
Skull is inside the fishing hut when you are playing as AJ, and it’s on your right side next to the broken cooker.
If you're still struggling feel free to use this as a reference.
The Walking Dead: The Final Season - Episode 4 CollectiblesHope this helped.