Just to add to Milla's comprehensive break down really!
There is an opportunity to buy some second hand uniform items and to discuss what uniform is essential/sizes etc. with other parents. I would highly recommend this if you are on a budget as some of the uniform is pricey (blazers etc. and rugby tops)
A note on blazers, do be careful if you are buying second hand as the girls' blazers button differently than the lads. I found the perfect one for him, at one of the events, only to discover at the last second before purchasing it was a young ladies!!
The skorts, for girls obviously, are also confusing by all accounts and getting the right size can be tricky (these are ordered online and so you have no real idea on size..ask someone with a girl at the school and they will keep you right)
There is also an option to have professionally fitted mouth guards for both boys and girls.
I was told that most of the boys do not wear jumpers and not to bother getting one. However, my DS (very skinny) was freezing in just a blazer and shirt. He loves his jumper, I bought a decent one from The Famous, and it has washed very well (it is so soft I often find him wearing it round the house at the weekend
Do take advantage of 'get togethers' organised by the school as they are very useful for getting to know people. I have certainly found it invaluable knowing some of the mums in my DS's class. When homeworks are confusing/lost/forgotten etc. they can help you out (Eh, Milla?
Think that's about it really
Relax and enjoy the ride