Click the paper on the desk. This is all Gus needs to put together the clues that point to the owner of PrintFax, who may be involved in all of the strange occurrences.
The Employees Only room in Good Deals. You can use the toy robot by the camera to keep the lights on.
The "Back Door" key fits the employees-only door at Good Deals Electronics. (use the toy robot by the camera to keep the lights on)
The code for the scooter is "FROST."
Not the back room of MacGuffin's, but the Employees Only room at Good Deals next door. Use the toy robot at the camera to keep the lights on.
If by security room you mean the "Employees Only" room of Good Deals, your next step is to go to PrintFax and ask some questions. However, you don't quite make it there.
Only Paid Monthly Members can get Early Access as of 2012-2013.
The only pictures are apparently the cards on the Bonus Quest. (see related question)
There is no back room there. Someone answered another question incorrectly. The "back door" key fits the Employees Only room at Good Deals. You will need to use the toy robot next to the camera there to keep the lights on.
You can use it in the Good Deals store, where the lights only stay on when something is moving in the front by the camera.
Not sure why you would, as this is not part of the island quest. You only go into the joke store (Jolly Gifts) as part of the Bonus Quest.
At the Good Deals store, the camera by the door is what keeps the lights on. You need the Toy Robot, which you have taken from Guiseppe's Toys. Go to your bag and set it down, and it'll keep the lights on. When you have the "back room" key that the thief dropped, open the door that says "Employees Only."
Go inside? There is a form on the desk that implicates the owner of PrintFax in some of the odd goings-on, and there must have been some reason for him to have a key to Good Deals (above Slugger's Keepsakes) and a lease on the empty store (below Slugger's Keepsakes). Head for PrintFax to question him.