Document in hand, left (8)
I believe the answer is:
passport
'document' is the definition.
(I know that passport is a type of instrument)
'hand left' is the wordplay.
'hand' becomes 'pass' (synonyms).
'left' becomes 'port' (left side of a ship - opposite of starboard).
'pass'+'port'='PASSPORT'
'in' acts as a link.
(Other definitions for passport that I've seen before include "Travel ID" , "you might need Visa with this" , "entry permit?" , "Document to allow entry to another country" , "that may gain acceptance" .)