Hello. I just had my interview last week. You can bring anything because you have to walk through a metal detector and have your bags scanned. You'll most likely be talked to like you're a criminal, but it'll be fine.
Good luck! Oh, don't forget to ask for the form N-652 after your interview whether you're approved or continued. It tells you the results of your interview. I wasn't given one and was told by someone on this forum that the adjudicator most likely forgot. Aargghh!
Usually they don't allow cell phones and music players into the USCIS offices. My guess is that if you carry your papers in a laptop bag they are going to assume you have a laptop and give you a harder time until you clarify the issue.
Leave the cell phone in your car. I think is better because they are really picky about this. There was this girl on the phone at the waiting area when I went to get my FP done and boy they told her off about this and they were NOT nice about it! I was waiting for a slap on her face by the security lady, ha! people dont listen some times!
I guess it depends on how "nutty" the guys are at the local DO office. At Newark DO, I walked in with laptop, cell phone, car keys etc. The guys at the main security just scanned everything, didnt even look at my appointment letter, asked to start laptop and show 'windows' and thats it.
Inside the build, on the Interview/Oath floor, the guy asked me to make sure cell phone is turned off. I even saw bunch of guys talking on the phone in the waiting area.
But again, it depends largely on how the local DO building is run.
Leave cellphone in your car. No laptops at all, just leave that at home or in the car in the trunk. There is no need to irk the people at the door. All that is required is you and you, plus all documents. No need to complicate issues early in the morning or the security guards might complicate things for you: denial of entry. Have you dealt with people who have miminal power and want to abuse it?