A clear pencil case is ideal but I am not sure they would allow the child to bring in a stop watch, or even a ruler! My son took his watch which he set out on the table next to him. It was useful in the 'old' Bishop Vesey exam when there was time to spare - but not at all useful for KE , when there is no time to spare anyway and you just go through it fast and steady.
Until this year, there were 2 separate exams of course. For the Bishop Vesey exam last year, children were told via letter to bring a pencil. I bought loads of really expensive ones as my son writes really hard and breaks them easily. I didn't want to waste his time with him sharpening them - so didnt include a sharpener. The examiner (who clearly had no spare pencils) saw them and decided to distribute them all to the many children who had turned up to the exam without any pencil - we only got one given back, and in fact the one he was left with broke, leaving him to soldier on through the latter part of the exam with a bent nib.
At the King Edward Grammar exam, we had been advised that he needed a snack but nothing else, he did again take in loads of pencils but the examiner gave every pupil one of theirs and he just used that. I made sure he had a few large erasers for each exam too - although there was some confusion about whether he should rub out or cross out wrong answers. In fact, he crossed out (being much quicker than rubbing) and a poster here was saying they should have rubbed, prompting a call to the Foundation office who assured me that crossing was fine too! I would advise my child to listen very carefully to the instructions, and ask if they are unsure about anything.
I think I went slightly mad on snacks at the time - I remember buying all sorts of ridiculously priced 'vitamin water' bottlesd and Innocent smoothies from tesco and fancy snacks to take in - must have worked as he's at Camp Hill now