Quietly one pockets 2/3 of bus fare in Japan (5)
I believe the answer is:
sushi
'fare in japan' is the definition.
'sushi' can be an answer for 'fare' (sushi is a kind of food). I'm not sure about the 'in japan' bit.
'quietly one pockets 23 of bus' is the wordplay.
'quietly' becomes 'sh' (both are used to tell someone to be quiet).
'one' becomes 'i' (Roman numeral).
'pockets' is an insertion indicator.
's3 of bus' becomes 'us' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'sh'+'i'='shi'
'shi' going around 'us' is 'SUSHI'.
Can you help me to learn more?
(Other definitions for sushi that I've seen before include "Rice and raw fish wrapped in seaweed" , "Raw fish dishes" , "Food from Japan" , "cold food" , "Cold rice dish, often with raw fish" .)