Bag containing small part for cook (9)
I believe the answer is:
casserole
'for cook' is the definition.
(casserole is a type of cooking)
'bag containing small part' is the wordplay.
I cannot quite understand how this works, but
'small' could be 's' (abbreviation - e.g. clothes size) and 's' is located in the answer.
'bag' could be 'case' (I have seen 'Overnight bag' mean 'case' so perhaps 'bag' could also mean 'case') and 'case' is located in the remaining letters.
'part' could be 'role' (eg a theatrical role) and 'role' is found in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for casserole that I've seen before include "Meat dish" , "So cereals may be used for this oven-cooked covered dish" , "(Food cooked in a) stewpot" , "Make a stew" , "Kind of stew" .)