I had my oath ceremony there a few months back. Family and friends are allowed in but make sure not to bring noisy kids with you because they may kick out noisy kids. Your "entourage" won't be allowed to sit with you though as they will be told to sit down either way in the back or where the jury usually sits.
They will give you a package with a few things in. I remember there was a passport application, a congratulation letter from President Obama, a brochure about voting, a copy of the oath and the lyrics of the Pledge of Allegiance which you will have to sing.
It's a courtroom so they do not allow you to carry cameras. I think you can take pics outside the courtroom but I am not really sure.
The ceremony is pretty long (mine was over 3 hours). They will collect everybody's GC and ask you yo sign your naturalization certificate separately which is takes a LOT of time.
The earlier you get there the better. They will give out the certificate based on the row you are sitting (if you are on the first row you will be one of the first to get your certificate and leave).
I thought it was costmary during oaths for them to call out loud the country where everybody comes from. They did not do that during my oath.
No snacks in the courtroom.
Everybody was very nice and courteous during the oath.
Just a word of advice, they probably sent you a questionnaire along with the letter saying where the ceremony was going to take place. When you sign it you'll see they want you to write down the location where you signed the questionnaire. Regardless of where you are put down Central Islip . No need to panic if you already put down another place. When they check your questionnaire they will simply ask you to scratch it off and put down Central Islip.
Central Islip is pretty far from the city. You can take the train which will take you to Central Islip Station and from there you can take a bus that will take you to the courthouse in about five minutes. You can also use google map to calculate how long it will take from your location to Central Islip.
Hope that helps and good luck with your oath.