Packed — with coal? (8,2,3,5)

'packed' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'coal?' is the wordplay.
I cannot really understand how this works, but
'coal?' could be 'sea' (sea coal is a kind of coal) and 'sea' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

'with' is the link.

Can you help me to learn more?