If you have an appointment just show up with the appointment letter. I am not aware if you can go early. Seems like some people in this forum think it's possible, but I don't know. They asked me for the following items:
1. Passport with I94
2. H1B visa
3. EAD (if you have it)
The security guard just looked at these items and then returned them to me.
Rgds,
sadiq