Did my N400 interview (Philadelphia) based on 3yr marriage to US citizen. I went alone per the appointment letter. I brought tax returns, birth certificate, and marriage license. He only asked for current green card, unexpired passport and appointment letter. He did not take any other paper work.
Interviewer called me back about 20 minutes after my appointment time. He made me swear to tell the truth. Immediately asked me the naturalization questions. Made me read a sentence. Made me write a sentence. After those were done we went through biographical and travel data from my application.
Left with him saying he has to "review the full file" then I will get an official decision. Process took less than 15 mins.