You can make a portfolio for your own "revision" I guess, but do not bring it in. If anything it would look like you're over-prepared and so your answers are rehearsed, not organic like they want. I had a small exercise book where I'd made notes on things like the Charlie Gard case and TED Talks I'd seen, but I only used it for preparation prior to the interview and I didn't bring it in with me.
Also, you can never guess what you'll be asked about (unless there's a set thing you're always asked about, e.g. UCL will pretty much always ask about your BMAT essay and something related to the NHS) so don't worry about learning miniscule details of one case. At my HYMS MMI I knew I was going to be asked about recent events so I'd looked in the news and things in the weeks leading up to my interview and rather than things like the flu crisis, I was asked about the new London GP app (which I had actually downloaded out of curiosity and read up on).
Don't bother sending a thank you letter either as they score you at the time of your interview usually so it will have no benefit to your application and tbh I'd be a bit weirded out if I was an interviewer. Just say "thank you" or "it was nice meeting you" as you leave, don't worry about sending a letter or note.
I'd recommend bringing a bottle of water, maybe a book to read depending on the style and timings of interview, any preparation notes you've done to look over whilst you're waiting and potentially a snack (once again depending on the style, I only mention this as I know that at UCL you may arrive for around 1pm but not actually be interviewed until around 5pm, so be prepared). Also tissues! I brought pretty much everything else to my UCL interview and as soon as I got there my nose started running!
Also, definitely bring any ID or emails they've requested like Bianica said!