In the future, share whatever part remains (6)
I believe the answer is:
offcut
'whatever part remains' is the definition.
(an offcut is a leftover bit)
'in the future share' is the wordplay.
'in the future' becomes 'off' (synonyms).
'share' becomes 'cut' (cut is a kind of share).
'off'+'cut'='OFFCUT'
(Other definitions for offcut that I've seen before include "bit of stick?" , "Remnant of material" , "Small bit of some material" , "Waste piece" , "End" .)