Sauce -- something sailor may use up (7)
I believe the answer is:
ketchup
'sauce' is the definition.
(ketchup is a type of sauce)
'use up' is the wordplay.
'use' becomes 'ketch' (I can't justify this - if you can you should give a lot more credence to this answer).
'ketch'+'up'='KETCHUP'
'something sailor may' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for ketchup that I've seen before include "Red sauce" , "Sauce made largely of tomatoes" , "Condiment" , "Spicy tomato sauce" , "Relish" .)