Documents for entry to US on B1/B2 visa

[r_g]

Hi,

I have a quick question. I have a valid B1/B2 visa valid till 2016 and with multiple entries. The annotation field is blank. In the last 3-4 years I have traveled to the US at least 4-5 times for official reasons. But this time I need to travel as a tourist for a week. Basically, I will be visiting my friend (who happens to be a student). What all documents (exhaustive list) do I need to carry to ensure that my immigration is smooth. Thanks a lot for all the help.

[kabkaba]

An informal invitation letter from your friend, your detailed itinerary (with hotel accomodations if any) and some proof of funds available for your trip.