The most common and most likely answer to this crossword clue is the 6 letter word UNSENT
I've seen this crossword clue in Independent
U
N
S
E
N
T
Buddy explains!
The straight part
We know that "Still to go" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case still to go = unsent.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does UNSENT mean?
UNSENT adjective- Not yet sent or transmitted.