Fireworks in crates? (7)
I believe the answer is:
bangers
I believe this clue is a double definition.
'fireworks' is the first definition.
(banger is a kind of firework)
'crates?' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for bangers that I've seen before include "Sausages" , "Loud fireworks" , "Crates" , "explosives?" .)