What convicts do half-heartedly, wanting cash by bank (8)
I believe the answer is:
porridge
'what convicts do' is the definition.
(porridge can mean time in prison)
'half-heartedly wanting cash by bank' is the wordplay.
'half-heartedly wanting cash' becomes 'por' (I can't explain this - if you can you should give a lot more credence to this answer).
'by' is a charade indicator (letters next to each other).
'bank' becomes 'ridge'.
'por'+'ridge'='PORRIDGE'
(Other definitions for porridge that I've seen before include "Morning oats" , "Or griped about the dish" , "Breakfast dish - spell in prison" , "Possibly breakfast - time in prison" , "Breakfast dish of boiled oatmeal" .)