If you're moving to secondary school you're going to need a lot more organisation because:
At primary school
You only have to remember stuff like: Book bag, PE kit, reading book and homework once a week.
At secondary school
You have more stuff to bring in every day than you used to have in a whole week.
There are five or more lessons a day. Each lesson has its own set of books and its own homework. If you want to remember everything you have to write it down.
The school may give you a planner. This will really help. Otherwise you will need to get a diary.