Before submission you need your research to be finished and your thesis to be done.
Before the viva you need to prepare your thesis and yourself. You need to read, to think, to speak and get ready.
In the viva you need your thesis, something to write on, something to drink and anything that will help you feel good in those few hours.
After the viva you need a way to celebrate – and you will need to celebrate!
And you might need other things, far more personal than I could know or guess. What do you need? How can you make sure you have them?