Father, with quantity of paper, wrapping unknown fancy (8)
I believe the answer is:
daydream
'fancy' is the definition.
(thesaurus)
'father with quantity of paper wrapping unknown' is the wordplay.
'father' becomes 'dad' (informal term for father).
'with' is a charade indicator (letters next to each other).
'quantity of paper' becomes 'ream' (a ream is a large amount of paper).
'wrapping' means one lot of letters goes inside another.
'unknown' becomes 'y' (algebra).
'dad'+'ream'='dadream'
'dadream' placed around 'y' is 'DAYDREAM'.
(Other definitions for daydream that I've seen before include "An idle diurnal fantasy" , "Diurnal reverie" , "Wool-gather" , "A pleasant diurnal fantasy" , "Indulge in a fantasy" .)