The only place I had an interview was Manchester. I had a really informal "chat" with my interviewer, mostly concentrated on going through the work I had bought with me, talking about it and then questions thrown in at random. The usual "what buildings do you like?/what's your favourite building?" or "who's work do you like?/who's your favourite architect?", so at least be prepared for those.
Tip: don't say a really famous or popular building, use one either known by architects but not necessarily by the "general" public or it could even be a building near where you live or somewhere you've travelled that they will have never seen or heard of (take some photos, taken by you) as it will show an interest in architecture, like your aware of it all around you even when your just driving around, walking in the town centre or something, rather than you just picked a well known building out of a book. Also, whatever you do, don't say Foster's your favourite architect!
All interviews are very different though, even within each school. My friends on my course have described very different experiences at their Manchester interview, more formal ones, with multiple interviewers, staff having older students with them asking questions to really informal chats with no direct questions at all, just more of a "getting to know you" session.
All I did to prepare was to read over my personal statement to remember what I had put (although it was never used or mentioned in my interview in the end) and looked over the work I was taking to try and think through what I could say about each piece if asked. It's worth thinking about what kind of questions you may be asked even if your not asked them, so as well as the above questions, think about why you want to study architecture, what you want to do (not every one wants to become an architect or even study past the first 3 year degree, for them it's just a "stepping stone"), what parts of the course you think you'll enjoy/be good at? Just try to convey as much enthusiasm for the subject as possible, architecture should already be at least a hobby, you should now want it to become a huge part of your life, not just a degree you want to do. Don't over do it though and don't practice answers, just have a rough idea what you want to get across and then talk about it in a normal way like you would in any conversation.
As for stuff to take, I just took a wide range of work I had done from my AS level Art and GCSE Art and Graphics. They did send a list of suggested work with the interview request which was helpful. Take work in different media, like different paints, pastels, pencils. Still life sketches, of buildings if possible, but anything that shows you can draw accurately will be fine, some abstract/semi-abstract work, 3D work particularly models (take photos if large), if you are good at photography take some photos of buildings (or parts of), take some written work (an essay from school will do - I took my A level geography coursework). I didn't have any CAD or photoshop work, but i'm sure they would be interested in it, just check the list they (should) send you.
When it comes to books I only buy the ones I like (so no boring ones with black and white pictures and too much writing!). When I accepted my place, I got sent (along with all the usual registration stuff) a reading list and equipment list. Out of the 25 books on the list I already owned 10 of them. I've been collecting architecture books for years and was glad that what I was interested in and enjoyed reading was actually relevant to the course. I looked up the rest of the books and found a few more quite interesting so I got those too, the rest I still haven't bothered with or I just got them out from the library for the couple of weeks they were actually needed for. Books I recommend because I have actually used them directly for doing work either by being told in a lecture to read it for the next project or finding it useful myself include:
Architect's Pocket Book by Charlotte Baden-Powell
Architecture: Form, Space and Order by Francis D.K. Ching
Architectural Graphics by Francis D.K. Ching
Building Construction Illustrated by Francis D.K. Ching and Cassandra Adams
A Visual Dictionary of Architecture by Francis D.K Ching
XS: Big Ideas, Small Buildings by Phyllis Richardson
Materials for Architectural Design by Victoria Ballard Bell (Author), Patrick Rand (Author)
Materials, Structures and Standards: All Details Architects Need to Know But Can Never Find by Julia McMorrough (Author)
The Story of Architecture by Norman Foster and Jonathan Glancey(Eyewitness Companion Guides)
Architects Today by Kester Rattenbury (Author),
Green Architecture: The Art of Architecture in the Age of Ecology (Architecture & Design) by James Wines (Author)
Analysing Architecture by Simon Unwin (Author)
40 Architects Around 40 (Klotz) by Jessica Cargill Thompson
(sorry that's about as many as I can remember right now, there's probably more)
Most of these are worth buying. Not all at once but as you go along, buying them as and when you need them. Most in first year, some in second year. The whole lot brand new would cost about £150 but i'm sure you can find them second hand. You will be referencing books all the time so always getting them from a library is not an option, especially if a book is mentioned as needing reading for the next project, 200 students cannot all read a book in the library if there are only 5 copies of it. If you have a general interest in architecture then you will probably find all of the above books interesting anyway. I owned 7 of them before I even applied to go to uni. The ones I bought later were the construction and materials books. There are loads of books to choose from on these topics (these are just the ones I like) and you will probably need at least one in order to complete your work. Any books with lots of pictures of buildings or elements of building that you like are useful because every project needs precedent ideas. However, these can be found in architecture journals as well, which the university library stocks every copy of, so with some books it's just a matter of convenience whether you want them permanently or not.
Sorry, i've gone on a bit (make that A LOT)! Hope I haven't overwhelmed you! Let me know any more questions.