What he is taking to hide a non-believer? (7)
I believe the answer is:
atheist
'a non-believer?' is the definition.
(someone who doesn't believe in God)
'what he is taking to hide' is the wordplay.
'to hide' indicates the answer is hidden within the clue.
'ATHEIST' can be found hidden inside 'what he is taking'.
(Other definitions for atheist that I've seen before include "Godless person" , "Person who believes there is no God" , "God denier" , "One not believing in gods" , "One denying existence of a god" .)