Country supplies plain oatmeal occasionally (6)
I believe the answer is:
panama
'country' is the definition.
(I know that Panama is a country)
'plain oatmeal occasionally' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
'plain'+'oatmeal'='plainoatmeal'
The alternating letters of 'plainoatmeal' are 'PANAMA'.
'supplies' is the link.
(Other definitions for panama that I've seen before include "isthmus" , "Land - hat - cigar" , "Hat made of plaited palm leaves" , "American canal or kind of hat" , "Hat woven from jipijapa leaves" .)