Hey, so this hasn't been made yet, so I guess I'll do it.
The collectibles aren't too difficult to find but definitely you might miss one or two if you're not actively searching them out.

Item 1/4 for Unannounced Game 1
As soon as you enter the doors to the expo, at the Nvidia booth to your left is the first collectible.









Item 1/4 for Unannounced Game 2
In the Carrion area, there's some stairs to the right of the exit, go up and it's right in front of you.









Item 1/4 for Unannounced Game 3
Before you enter the Weird West area, there's a trash bag lying to your right between the drones.









Item 2/4 for Unannounced Game 2
When you enter the Weird West area, there's some stairs to the left of the screen that leads to a bar, the cup is there.









Item 2/4 for Unannounced Game 1
As soon as you exit the lift, it's directly in front of you on the boxes.









Item 3/4 for Unannounced Game 2
When you enter the room with the credits, there's a desk with the cup on it to your left.









Item 3/4 for Unannounced Game 1
Going through the vent, the book will be in between the two possible paths.









Item 4/4 for Unannounced Game 1
Inside the Blightbound area, the book is lying on one of the game booths.









Item 2/4 for Unannounced Game 3
At the entrance of the Olija area, the trash bag is on the spear to the left.










Item 3/4 for Unannounced Game 3
To the right on the Serious Sam 4 stage, lying next to some blocks.









Item 4/4 for Unannounced Game 2
Inside the Fall Guys area, to the left of the exit there's some stairs. On a table in this above area is the final cup.









Item 4/4 for Unannounced Game 3
Inside the temple past the Shadow Warrior 3 trailer, there's a statue on the right with the trash bag on it.