This can really really turn things into a headache for you... If at all possible I would ship everything via UPS or FedEx (even brochures) - That way you're only presenting yourself at customs.

Last time I travelled to the USA to a trade show the questions went something like this:

US Officer: Do you have any materials to exhibit?
Me: No
Officer: No samples?
Me: No
Officer: Not even brochures?
Me: No, everything was FedExed ahead and is meeting me at the show.
Officer: Good. That's how it's supposed to be done. Have a good trip.

I realize I broke a cardinal rule in interacting with customs by providing more information than what was specifically requested (I should have just said "no") but it seemed to speed up the process...