A coffee to go....( for syntax experts)
Could the infinitive phrase "to go" be a complement of the noun phrase "a coffee"?
Yes, I can't see a problem with that.
However, it is normally unnecessary - it makes no difference to the server if it is to go or you will drink it in the shop - it typically is "to go". If, however, it is a shop that offers ceramic cups for non-takeaway, you do need to specify.