I conduct interviews at my office as well. Be prepared with your resume and list of references, and yes, I think it would be a good idea to add your volunteer activities. Personally, I think that shows a lot about a person -- that you take initiative. Also, study your resume (know the dates you worked at other places, etc.) and have an extra copy in front of you to refer to. We recently interviewed someone who couldn't even get the dates right on a job she worked less than 2 years ago, and she didn't bring a copy of her resume and reached over to look at MY copy!!
For the references, I don't think it would hurt to add a personal, non-work related reference. And ditto what EthansMom said about calling your references. You would be amazed how many references we contact that seem "shocked" that they were listed as a reference!
Be yourself, be honest, and if possible, show how your qualities and skills can relate to the job you're applying for (but don't overdo it -- some people go on and on about how great they are, but they end up being a let down).
I would also try and do a little research on the company, esp. if you don't know much about them. We are always impressed by people who at least make some kind of effort to find out a little more about us, even if they didn't get very far.
If your job involves working with other people at any level (even if it's just co-workers and not necessarily external clients), mention something about your people skills. In my office, it's extremely important to find someone who has pretty good people skills. We are turned off by people who only talk about skills and qualifications and say nothing about their ability to work with others.
You may want to do an online search for interview tips and practice answering some typical interview questions like what your strenghts and weaknesses are, why you want to work there, etc. (Personally, and I'm pretty sure my office is an exception, but we tried to stay away from the typical questions -- however, it can only help you to be prepared, and you may be able to tailor some of your responses to the practice questions to the real questions that are asked.)
Anyway, I could go on and on because in my office, we go through a pretty intense interview process since it's really important that people "fit in," but I'll leave it at that for now. Good luck!!!
