You are not officially allowed to have any fizzy drinks on SnS. However, Coke Zero doesn't contain any citric acid and won't take you out of ketosis so it is one of the few fizzy drinks that won't be a problem. It is full of nasty chemicals though - yuck!
My parents livein Cornwall (so not too far from Devon) and when I went to see them in December my mum didn't recognise me getting off the train and she was only a few feet from me! Mind you - my mum is a bit doo lally.