There’s a lot you can do during viva prep. Some tasks and activities are essential, some are optional and some depend on how you feel about your work (or the specifics of the work itself).
Always start the period of viva prep by reading your thesis. Whatever plan you make, make reading your thesis the starting point.
Don’t rush, don’t skip or skim, but take some time to refresh your memory before you do all of the other things.
Making notes, annotating margins and reading one more paper can all wait until after you have made the solid foundations of reading your thesis.