- Passport (including all the old ones)
- Green card
- Original or copy of the documents that you filed with your N-400 (you want to have everything that you submitted because you are expected to know what you provided and be prepared to answer any questions)
Now, I am assuming that yours is a simple case. If it is not and you have such issues as arrests or deportations or court cases or other mess in your immigration history, while you may have provided most of the documentation in your application, it is better to have all the files related to these matters in a separate bag (I suggest that you keep the documents in the list above in your hand so that you have them handy when showing them and everything else is a backup in a bag that you will most likely not need to take out but you will be ready; I also suggest that you organize these papers in separate files with markers so that you can pick the right document in one second, for example, mark the papers as Arrest 2004 or Asylum 1999).
Other thing to remember is not to show any thing more than you are asked to show. The officers are smart people and they know what they are doing. If they need something they will ask for it. If they don't, it simply means that they are satisfied with what they have on your record. If you try to dump documents not asked for on the officer, most likely you will create a situation in which the officer will simply grab the file and decide to review it later (they have appointments scheduled and have a definite amount of time allotted for each interview so they might simply refuse to give you a decision on the spot).