Supply ultimate in wise crack (5)
I believe the answer is:
equip
'supply' is the definition.
(I know that equip is a type of supply)
'ultimate in wise crack' is the wordplay.
'ultimate in' suggests the final letters.
'crack' becomes 'quip' (both can mean a joke).
The final letter of 'wise' is 'e'.
'e'+'quip'='EQUIP'
(Other definitions for equip that I've seen before include "Give everything needed" , "Supply (with kit)" , "Give kit to" , "Pique (anag.)" , "Furnish, fit out" .)