This paper is basically just testing what you know about Geography and such, so I just recommend knowing your stuff and don't forget any case studies because you may still be able to use them.
If you're good at the other units then you should be able to do Unit 3 with ease as its mostly about applying what you've learnt to a new situation that you may not have seen.
I did the exact same course at GCSE and unit 3 was my best Geography exam because it suited me more, since it wasn't about hard core remembering and fact stating, however you do still need to quote as many facts as you can with the figure number etc.