From bygone days, a staple in the kitchen cupboard (5)
I believe the answer is:
pasta
'staple in the kitchen cupboard' is the definition.
'pasta' can be an answer for 'staple' (I have seen 'Italian staple ' mean 'pasta' so perhaps 'staple' could also mean 'pasta'). I am not sure about the 'in the kitchen cupboard' bit.
'from bygone days a' is the wordplay.
I cannot really see how this works, but
'bygone' could be 'past' (similar in meaning) and 'past' is found within the answer.
'a' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for pasta that I've seen before include "Fare from Italy" , "Italian cooking staple" , "Eg, spaghetti" , "Flour and water foodstuff" , "Dried flour paste for making Italian food" .)