There are 4 hidden items to collect and you can gather them as soon as you get off the ship. They are all brown and when you are near them they prompt you to hit Enter to pick them up. They are:
- Box (Not sure what it actually is, a six pack maybe?)
- Bunny
- Sunglasses
- Star
The
Box is behind you, on the dock near the two men and the stack of crates. You will see it on top of a crate right in front of the guy on the dock.
The
Bunny is to your left when you come off the dock, near the barn and Oswald, the carpenter. You will see it in the back corner, behind the horses and cart.
The
Sunglasses are to the right when you come off the dock. You will pass 2 men sitting on the edge on your right and then you will pass a cart and a stack of barrels. The sunglasses are directly ahead of you on a broken down cart in the sand.
The
Star is the hardest to find. It is behind the building to the left of where you picked up the Sunglasses, near a giant boulder.
**Multiple people in the comments have confirmed that picking up a single collectible by mashing either 'Enter' (on keyboard) or (on controller) will trick the game into thinking you picked up 4 collectibles and unlock the achievement.**