There is no reason to get nervous for this meeting. The trustee who runs the meeting is not a judge, and no final determinations are made at this meeting. Your lawyer will be with you, and the trustees are usually pretty nice. You are not in a courtroom. You are in an informal meeting room. Just relax, and follow the lead of your attorney.
What to wear
I recommend that my clients dress casually. You are not going into a formal courtroom setting. This is an informal meeting. Dress casually and do not wear anything "flashy."
What to Bring
Ask your attorney, but in most jurisdictions, all you need to bring are your photo ID (drivers license will work) and social security card. If you do not have a social security card, go order one before the meeting. When you order one, you will get a piece of paper that is proof of your social security number. You can use this. But definitely clear all this with your attorney ahead of time.
How to act and what to say
Either the trustee or your attorney will ask you the questions. Most are "yes" or "no" questions, but one question is "Why did you have to file for Bankruptcy?" Just sum it up in a few sentences. They do not want to hear your whole life story. Speak clearly, calmly, and very polite. Be honest with all your answers. You are under oath. Lying under oath in a bankruptcy proceeding is perjury and people go to jail for it. It is much better to have the trustee take some of your unexempt property, or to deny your bankruptcy, than to sit in Federal Prison for lying to a trustee.
The 5th Amendment
This almost never comes up, but if you feel like your testimony is going to get you convicted of a crime, stop talking and say "I am pleading the 5th amendment." This comes up when someone perhaps lied on financial statements to get loans that they are now putting into a Bankruptcy. Lying on financial statements that are submitted to an FDIC insured bank is a crime. If your testimony is asking you about this, then stop talking.