Terrible canteen's stocking American food (10)
I believe the answer is:
sustenance
'food' is the definition.
(sustenance is a kind of food)
'terrible canteen's stocking american' is the wordplay.
'terrible' indicates anagramming the letters.
'stocking' is an insertion indicator ('stock' can mean 'carry' or 'contain').
'american' becomes 'us'.
'canteens' is an anagram of 'stenance'.
'stenance' placed around 'us' is 'SUSTENANCE'.
(Other definitions for sustenance that I've seen before include "Food and drink" , "Nourishment" , "cooking provides this?" , "Nutriment" .)