Store up, perhaps certainly without certainty! (3,2)
I believe the answer is:
lay in
'store up' is the definition.
(I've seen this in another clue)
'perhaps certainly without certainty' is the wordplay.
'perhaps' is an anagram indicator.
'without' suggests deleting specific letters.
'certainty' becomes 'cert' (cert is a kind of certainty).
'certainly' with 'cert' taken out is 'ainly'.
'ainly' with letters rearranged gives 'LAY IN'.
(Other definitions for lay in that I've seen before include "Store" , "Acquire (a supply of)" .)