Good morning Tracer:
Officer never asked me for my tax return documents but my friend who was interviewing the same day, she was asking to shown. What I bought with me for interview: interview letter, green card, Calif DL, 3 years of my tax record, most current paycheck copy, all of the old passports and visas. During the interview, office went though your N400 application questions as you mailed it out. So it is always good to keep a copy for yourself. 10 questions from Zzz 100 questions list, I was only asked 6 out 10 cos I got all right for the first 6, asked me to write one sentence, and read on sentence. The whole process was simple, friendly, and in the very good timely matter. If you have any records, such as DUI... just let the officer known, not a big deal. My friend had to go to court and local police Dept request a statement for her DUI. Lucky me! I don't drink lol.
I apply as Single person, no family, no kids so maybe that is why my case was only 3 months. All I remember and Shock, 4 days after my interview.. Tada.. Oath letter. ^_^