You should be receiving a kit-list soon, if you don't up to 2 weeks before your first trip do get in contact with your Team Leader as they should by then have one themselves.
-Sunscreen
-Hat
-pjs
-plenty of underwear changes
-2 towels
-Trousers/ Long shorts suitable for outdoor activities. If you only have shorter shorts, consider buying leggings to wear underneath as you can't have bare legs whilst wearing a harness, which (depending on your activities) you will probably have to wear at some point.
-Plenty of socks
-2 pairs of shoes that you don't mind getting wet/ mucky
-tops/ t-shirts that you can easily move around in/ be active in
-They say not to bring snacks sometimes but my team did and it wasn't a problem, although your team leader probably has to make sure you're eating at meal times because you're their responsibility and they can't let you take part in a physical activity if they don't think you have enough energy, so don't fill yourself up so much that you can't eat at meal times!
-Deodorant
-Toiletries
-An extra blanket/ pillow (although even when camping you should be provided with a sleeping bag, this may be different across the country so do double check)
-A bottle that you can refill for water, cannot tell you how many times I had to go on water runs for my very disorganised team
-Any medication you need/ might need, although be sure to let your Team Leader know what these are as they will need to hang onto them if they are prescription, it's just the policy.
DON'T bring anything valuable. Seriously, your Team Leader can't be responsible for it. It is completely at your own risk that you bring something like that.
DON'T bring drugs or alcohol, you will be kicked off the site, there's a zero tolerance policy.
DON'T have sex on camp. I know it sounds silly but boys and girls can't even be in each other's rooms/ tents. If you really want to have sex, do it when you get home please! Again another zero tolerance issue. If you get caught having sex or with drugs/ alcohol your parents/ guardians have to be notified and we have to tell them why you're being kicked off, which can get very embarrassing for members of the team.
Despite those last "don'ts", the NCS programme is SO good, I had an amazing time and I was doing all the organising/ work that goes on behind the scenes so to speak, so it shouldn't have been fun for me but it really really was!
Hope this helps, let me know if you need to know anything else!