"To go" is American English, used in the US and Canada.
"To take away" is the phrase that's most used in Britain, Ireland, Australia and NZ. I'd say 'Take away', but I wouldn't be surprised to hear 'to go', especially in an American-style outlet or from younger people.
He said - what?!
- to go
- to go?
- I don't know what do you want! Do you whant "Take away"?