Vehicle outside gala, one with ace facility for refreshments (9)
I believe the answer is:
cafeteria
'facility for refreshments' is the definition.
(a cafeteria provides refreshments)
'vehicle outside gala one with ace' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'outside' means one lot of letters goes inside another.
'gala' becomes 'fete' (both can mean a festive event).
'one' becomes 'I' (Roman numeral).
'with ace' becomes 'a' (abbreviation. I am not sure about the 'with' bit.).
'car' going around 'fete' is 'cafeter'.
'cafeter'+'i'+'a'='CAFETERIA'
(Other definitions for cafeteria that I've seen before include "Where one scoffs" , "cheap restaurant" , "Canteen" , "Self-service eating place" , "greasy spoon?" .)