Pack small digit, say (4)
I believe the answer is:
stow
'pack' is the definition.
(stowing is a kind of packing)
'small digit say' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'digit' becomes 'toe' (digit on a foot).
'say' indicates a 'sounds like' (homophone) clue.
'toe' is a homophone of 'tow'.
's'+'tow'='STOW'
(Other definitions for stow that I've seen before include "Place in storage receptacle" , "Put away for storage" , "Author, -- Asimov" , "Deposit" , "Store away tidily" .)