Tuck sides of robe into luggage (6)
I believe the answer is:
'tuck' is the definition.
'sides of robe into luggage' is the wordplay.
'sides of' suggests removing the centre (only the letters on the sides remain).
'into' means one lot of letters goes inside another.
'luggage' becomes 'case' (I've seen this in other clues).
'robe' with its middle taken out is 're'.
're' inserted into 'case' is 'CREASE'.
(Other definitions for crease that I've seen before include "Wrinkle on the cricket pitch?" , "Fold, maybe unmeant" , "Fold in clothing" , "iron this out" , "Cricket pitch marking" .)