Tube fare - you've got nothing without it! (7)
I believe the answer is:
sausage
'tube fare' is the definition.
'sausage' can be an answer for 'fare' (sausage is a kind of food). I'm unsure of the 'tube' bit.
'nothing without it' is the wordplay.
I cannot quite see how this works, but
'it' could be 'sa' (old-fashioned abbreviation for sex appeal) and 'sa' is located in the answer.
The remaining letters 'usage' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'you've got' acts as a link.
Can you help me to learn more?
(Other definitions for sausage that I've seen before include "Part of a hot dog" , "Minced meat product" , "Assuage (anag.)" , "Minced meat and fat in cylindrical skin" , "Assuage with tasty meat roll" .)