Leftover rum intended to be picked up (7)
I believe the answer is:
oddment
'leftover' is the definition.
(I've seen this before)
'rum intended to be picked up' is the wordplay.
'rum' becomes 'odd' (rum can mean strange or dubious).
'intended' becomes 'meant' (to mean something is to intend it).
'to be picked up' shows a homophone (sound like) (I've seen 'is picked up' mean this (pick up can mean to hear)).
'meant' is a homophone of 'ment'.
'odd'+'ment'='ODDMENT'
(Other definitions for oddment that I've seen before include "Remnant" , "Left over item" , "a bit spare" , "Just a bit left" , "One of a broken set" .)