All good advice above Keith, as usual
We recently had our first surveillance audit for 18001 and I soaked up every ounce of experience from the auditor I could. He was great, in fact, it felt like he was teaching me for two days!
The main thing I'd take out of the comments above would be the honesty part. We also made use of our plasma screens for this approach to inform all on site that they may be asked questions by the auditor and if they didn't know the answer, just to say so. It's perfectly OK to not know the answer.
After all, the purpose of the audit is continual improvement, so learning is essential.
You will be fine.