Sorry lola, diet coke has citric acid which knocks you totally out of ketosis.
When you get the water flavours they are nice with fizzy water, not quite diet coke, but they are like fizzy pop.
You can have them hot too which is great when it is cold out.
You can also have peppermint or nettle tea.
peppermint is nice, I need a sweetener in it, you can have that hot or put it in the fridge and have it with ice. Will be nice when the weather warms up a bit.