Picked up post and something for dinner (5)
I believe the answer is:
steak
'something for dinner' is the definition.
'picked up post' is the wordplay.
'picked up' shows a homophone (sound like).
'post' becomes 'stake' ('stake' can be a synonym of 'post').
'stake' is a homophone of 'STEAK'.
'and' acts as a link.
(Other definitions for steak that I've seen before include "pale by the sound of it" , "Cut of meat or fish" , "Thick slice of meat" , "Takes (anag.)" , "High quality beef" .)