Share out a fee for passage on the way back (5)
I believe the answer is:
allot
'share out' is the definition.
(allotting is a kind of sharing out)
'a fee for passage on the way back' is the wordplay.
'fee for passage' becomes 'toll' (as in a toll for passing over a bridge).
'on the way back' is a reversal indicator.
'toll' written backwards gives 'llot'.
'a'+'llot'='ALLOT'
(Other definitions for allot that I've seen before include "Distribute in portions" , "Assign or distribute" , "Hand out" , "Dispense or distribute" , "Give, apportion" .)