Picked up second person's stock item (3)
I believe the answer is:
ewe
'stock item' is the definition.
(stock can mean farm animals)
'picked up second person's' is the wordplay.
'picked up' indicates a 'sounds like' (homophone) clue.
'second person' becomes 'you' (second person pronoun).
'you' sounds like 'EWE'.
(Other definitions for ewe that I've seen before include "Language" , "Lamb supplier" , "One needing pastoral care" , "Female animal" , "Farm animal" .)