Hi Mgee
First of all I hope everything goes well for you at the hospital. No need to bring any extra clothes unless you think they are going to admit you for an overnight stay, and by the sound of it you are going there to talk about future admissions so I doubt they would admit you straightaway. So I think wearing something really comfortable and easy to get on and off quickly is the best idea and make sure you dress warmly enough, if you're kept sitting and waiting (I hope that you're not), you don't want to get cold. Probably a good idea to bring a list of any prescription medications you take and if you have copies of consultants' letters or diagnostic test results from abroad they might be useful to bring along. As you're in Wellington I assume you're not going to Waikato Hospital (where I work) otherwise I would offer to meet you for a cup of tea or help you out with directions.
I hope everything goes smoothly for you!
Bridget