Leaves boat renovated by Carnegie's first company (7)
I believe the answer is:
tobacco
'leaves' is the definition.
(tobacco leaves)
'boat renovated by carnegie's first company' is the wordplay.
'renovated' is an anagram indicator.
'by' is a charade indicator (letters next to each other).
'carnegie's first' becomes 'c' (1st letter of 'carnegie').
'company' becomes 'co' (abbreviation).
'boat' with letters rearranged gives 'toba'.
'toba'+'c'+'co'='TOBACCO'
(Other definitions for tobacco that I've seen before include "New World product" , "Popular narcotic" , "20 [CASTRO] 's favourite leaves" , "Plant with narcotic leaves" , "(Treated leaves of) American plant" .)