Mind part of drink before journey (8)
I believe the answer is:
superego
'mind part' is the definition.
'drink before journey' is the wordplay.
'drink' becomes 'sup' (I've seen this before).
'before' becomes 'ere' (usually literary).
'journey' becomes 'go' (I've seen this in other clues**).
'sup'+'ere'+'go'='SUPEREGO'
'of' acts as a link.
(Other definitions for superego that I've seen before include "self-critic" , "See group (anag.)" , "Internal monitor of psyche" , "self-criticism?" , "Part of the unconscious mind - pose urge (anag)" .)