Small bag with a cold explosive hidden in street (6)
I believe the answer is:
sachet
'small bag' is the definition.
(I've seen this before)
'a cold explosive hidden in street' is the wordplay.
'a cold' becomes 'ac' (I've seen this in other clues**).
'explosive' becomes 'he' (abbreviation for high explosive).
'hidden in' means one lot of letters goes inside another.
'street' becomes 'st'.
'ac'+'he'='ache'
'ache' placed into 'st' is 'SACHET'.
'with' acts as a link.
(Other definitions for sachet that I've seen before include "'Small soft packet, of pot-pourri perhaps (6)'" , "Sealed plastic substance container" , "Small envelope-like container" , "Sealed bag or packet" , "Chaste as a sealed plastic bag" .)