Traveller might have one go left (8)
I believe the answer is:
passport
'traveller might have one' is the definition.
'go left' is the wordplay.
'go' becomes 'pass' (synonyms).
'left' becomes 'port' (left side of a ship - opposite of starboard).
'pass'+'port'='PASSPORT'
(Other definitions for passport that I've seen before include "Document facilitating travel" , "Document allowing travel abroad" , "Document to allow entry to another country" , "Travel ID" , "Travel doc" .)