They hang from trees, and pack a change of kit in metal boxes (7)
I believe the answer is:
catkins
'they hang from trees and pack' is the definition.
The definition suggests an adverb but the answer is not.
'a change of kit in metal boxes' is the wordplay.
'a' becomes 'an'.
'change of' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'metal' becomes 'cs' (Cs is an example).
'boxes' is an insertion indicator (the outside letters must 'box' inside letters in).
'kit' is an anagram of 'tki'.
'an' enclosing 'tki' is 'atkin'.
'atkin' put inside 'cs' is 'CATKINS'.
Can you help me to learn more?
(Other definitions for catkins that I've seen before include "They hang on willows" , "Hanging spikes on a willow tree" , "Hanging spikes on willow trees" , "Hanging flowering spikes, of willow perhaps" .)