Choices underpinning island church's help for climbers (3-5)
I believe the answer is:
ice-picks
'help for climbers' is the definition.
(aids when rock climbing)
'choices underpinning island church's' is the wordplay.
'choices' becomes 'picks' ('pick' can be a synonym of 'choice').
'underpinning' says to put letters next to each other (I've seen this in other clues).
'island' becomes 'i'.
'church' becomes 'ce' (abbreviation for Church of England).
'i'+'ce'='ice'
'picks' put after 'ice' is 'ICE-PICKS'.
(Another definition for ice-picks that I've seen is " tools for alpinists".)