All of these items are story related, except 3. You will probably pick these up anyway. All three of these items are usable in the game, and you'll NEED one of the first two lights to realistically move on. Every other item is REQUIRED for the story.
-Polaroid. It's in the Master Suite. You can see it early, but you can't pick it up until you need to find the crawlspace in the story. (I'm being purposefully vague, but you'll know it when that is.)
-Dynamo flashlight. On the way to the crawlspace. You will literally be RIGHT NEXT TO IT in the closet before you enter the crawlspace.
-Later, when you go into room 117 (also part of the story), you'll find a Parabolic Microphone that you can pick up.
The achievement won't pop until you find the last story related item in Day 9. Not giving it away.