Company's kept unionist doubled up on food (8)
I believe the answer is:
couscous
'food' is the definition.
(I've seen this before)
'company's kept unionist doubled up' is the wordplay.
'company's' becomes 'co's' (abbreviation).
'kept' indicates putting letters inside.
'unionist' becomes 'u' (abbreviation as in Democratic Unionist Party).
'doubled up' shows that letters should be duplicated.
'cos' going around 'u' is 'cous'.
'cous' duplicated is 'COUSCOUS'.
'on' is the link.
(Other definitions for couscous that I've seen before include "African dish of crushed and steamed wheat" , "food" , "African dish of crushed steamed semolina" , "Form of semolina" , "Semolina grains" .)