Inside bag, heroin for cabin (5)
I believe the answer is:
shack
'for cabin' is the definition.
(I have seen 'Rough cabin ' mean 'shack' so perhaps 'cabin' could also mean 'shack')
'inside bag heroin' is the wordplay.
'inside' indicates putting letters inside.
'bag' becomes 'sack' (both can mean a container).
'heroin' becomes 'H' (H is a slang term for heroin).
'sack' going around 'h' is 'SHACK'.
(Other definitions for shack that I've seen before include "Rough hut or cabin" , "grim lodgings" , "Hovel" , "Crude dwelling" , "Crudely built hut" .)