Hey, I did exactly the same BTEC course as you, so I can help!
Most of the time, you're going to be sat at a computer, so you don't need a notepad or markers, just take a pen in case you need to sign something.
You're going to need a USB, because you might want to put some college work on it, so you can carry on doing it at home.
The bags mainly on your preference, but I'd recommend you take a smaller one because you won't be carrying much around, and you won't want a big bag bothering you.
You should always charge your phone up too, because it can sometimes get boring on those long breaks, so having some games to play or internet to surf can make the time go faster, and is a great conversation starter because it's easier to make lots of friends quickly on a computing course if you're a gamer.
Hope you enjoy the course and learn lots about computing!