My DD sat the test last November at CCHS so I will try and answer what I can!
Not sure about highlighter pens or spare paper might be best to check with CSSE. In our letter from the CSSE we were told to bring a pen, pencil, eraser and a ruler.
There were two sittings at CCHS last year. We were in the second sitting which was taken at CCHS and we had to arrive between 9.45 and 10.15 for the 10.30 exam. The first sitting of the exam was taken at the neighbouring School, St. Benedicks and I believe the time of this exam was 1 hour before?! I am sure somebody will correct me if I'm wrong! I believe the sittings were allocated alphabetically by your surname, therefore if your surname starts with an A,B,C etc you were allocated St. Bens if you were the other end of the alphabet you were allocated CCHS.
On arrival at CCHS my DD was allocated a number. I was asked to take my child through to the dining area where there were numbered tables. My DD was left at a numbered table with a current sixth form student whilst they waited for others to arrive. Parents are then asked to exit through the back of the dining room swiftly. My DD said that once everybody in her group arrived they were taken to a classroom by the sixth form students and played a few games, until they were called. My DD was then taken to the hall (her allocated area). The exams were sat at CCHS in either the main hall or the gym.
English was the first paper and after this paper they were asked to remain at their desks but were given a drink and a biscuit and I believe we're allowed to visit the toilet if needed. They then sat the maths paper. My DD's allocated time meant that she was at the school during the lunch period, we were told in our letter from the CCSE that we could supply them with lunch if we wished but that it needed to be something small as they only had about a 10 minute break for eating and drinking. She had her sandwich and then was allowed outside and was allowed to find any friends. They were then called back to their allocated place, the hall or gym to finish the last paper, the VR. The exam ran over by about 10 minutes.
Hope this helps
Try to visit the school where they will be sitting the exam as many times as possible so that they feel familiar with their surroundings. I also talked to my DD on the tour of the school about the possibility that she may sit in either the gym or the hall whilst we were in these rooms, again to try and familiarise her with both of these rooms and luckily for us she was allocated the hall!
I have to say I was very impressed with the organisation of the day, the school do a fantastic job and the children are really looked after.
Best of luck to you and your DD! The big day will soon be here now........