During the course of the game you will unlock items for a total of 200 items per game. There is a total of 500 items in the game so there is some RNG involved with getting blocks that will complete the set.
Once you have four of the similar items you will need to group them together. You can either hold all four at the same time or place them next to items that are already on the floor.
These are the items I used to unlock All the Camels
- Full Camel (Dark yellow with yellow background)
- Camel Humps (Two yellow humps on a blue background)
- Camel Prints (Brown hoof marks on a yellow background)
- Camel Head (Purple background)
I had all four of these items at the start of my second game, I just had to place them together to pop the achievement
The best time to match these up is during the untimed "Stock Take" phase of gameplay.
Also you can revisit warehouses that you completed.