Coke zero is VILE I am afraid so I don't have it.
Chewing gum....try it. see if it makes you hungry, if not then fine.
Flavoured waters, this is completely unofficial and I'm sure I'll get told off again, but in the real world you may well find you are ok with things that have MALIC acid rather than those that have CITRIC acid. just check the label. they're a bit few and far between but they do exist.
Citric acid can play hell with ketosis, malic acid seems to be ok. But as usual, if it stalls your loss, then stop. Everyone is different!