Every one is packed in a tea chest (4)
I believe the answer is:
each
'every one' is the definition.
(I've seen this in another clue)
'packed in a tea chest' is the wordplay.
'packed in' says the answer is hidden in the clue.
'EACH' is hidden in the letters of 'tea chest'.
'is' acts as a link.
(Other definitions for each that I've seen before include "every one individually" , "every individual" , "This way for a place" , "Per person" , "Every one of a number" .)