One Dog Story

There are 12 collectables in the game. They are typically some pop culture themed item (mostly video game related).

I wrote locations down as I was playing for reference (in case I had to recollect them on future runs).
Unfortunately, the notes were mostly for my own reference and I didn't describe them in perfect detail.

But, I figure it is better than nothing. If you guys would like to make notes in the comments, I would be more than happy to edit the solution to make it easier for future players.

NOTE: You only have to pick up a collectable once. In future playthroughs, any collectable you picked up will not be there second time around. Even if you pick up a collectable and die before a save spot, the collectable will remain collected.

I don't remember which item goes with each number (sorry), but I did manage to find them all on my first playthrough, so they are in order:

#1: In a room next to a save machine and scientist. Once you enter the door, it should be lying in the open (crowbar I believe). It is relatively early in the game.

#2: There will be a water section early in the game. At the end of the section, you will drain the water. Use the sniff technique ( in this area (possibly the very next room). It will be behind a hidden wall.

#3: In Calvin's Room (the brain in a jar)

#4: In the room where you find the Double Jump powerup

#5: Shortly after meeting EO-42 (yellow clothed dog), it will be hidden in a wall near some fans (use )

#6: In the Greenhouse section of the game. Just after using the red key card. Use in these areas to find it.

#7: In the room with the Rocket Launcher (in the wall to the right)

#8: After the fight with EO-42, room with the blue key. It is out in the open sitting on top of a machine.

#9: In the room with the 4 red buttons that you must move boxes onto. When you move a couple of the boxes, you will see the item behind them.

#10: In the space level. It is in a door near the bottom of the screen to the right (there are some spikes in this area). If using the rooms with crystals as a reference, I believe it is between crystals 2 and 3.

#11: Once you leave the space section and you are in the future, you will take an elevator up and there will be some rooms up here. The room on the right is full of spiders and there is a machine with an item sitting on top.

#12: The very last area of the game. There are a lot of rooms here with characters you met along your journey. There is a door in the bottom right corner that leads to some water rooms. Follow these and find the collectable at the end.

Hope this is of some help.