Things to pack while traveling alone internationally as a minor?

Hey. I am planning to go to England sometime this august and need a nice list of things to take, and how to keep organized. How to pack light and what to take on board... Electronics, books, etc. Also what will a airline supply me with... What will I have to pay for on the plane? It is about a thirteen hour flight. I am thirteen and I am going to visit some cousins for two weeks. Thanks for the answers and sorry for all the questions. I am really excited and want to be REALLY prepared. I have a passport and everything and also what should I do about cash. Should I take a credit card? My parents would be fine with that. I'm responsible haha. Yea. And also I have no idea about the weather there... My parents are researching about this stuff with me but their slow.... Thanks!