Basically whatever they ask for. I believe a PC will first make a visit to your house, and ensure that you reside there. He will also get the signatures from the reference people in the neighbourhood. He will then ask you to report to the police station on a specified date, and will mention what documents you need to carry. At least, this was what was told to me when I visited the police station a couple of days ago. The policeman asked me to wait for the physical verification, and then report to the station.
In addition to the documents provided at the passport office, he told that I would need to carry handwritten letters from the references saying that they know me for n number of years, and that they know that I do not have any cases in my name or that I am not affiliated to any political/criminal organisation. He also mentioned that I would need to get them attested at my local Village Officer.