Dead crummy jam one put in a sandwich? (4,6)

I believe the answer is:

dill pickle

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'one put in a sandwich?' is the definition.
I can't judge whether this defines the answer.

'dead crummy jam' is the wordplay.
'dead crummy' becomes 'dill' (I can't justify this - if you can you should give a lot more credence to this answer).
'jam' becomes 'pickle' (synonyms).
'dill'+'pickle'='DILL PICKLE'

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