Drink, spirit mostly, that's kept in a fancy wagon (9)
I believe the answer is:
lambrusco
'drink spirit mostly' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'that's kept in a fancy wagon' is the wordplay.
I cannot really understand how this works, but
'that's' could be 'sc' (short for Latin scilicet- 'it follows' or 'that is) and 'sc' is located in the answer.
'a' is within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for lambrusco that I've seen before include "Sparkling Italian wine" , "Type of Italian wine" , "Medium sweet, semi-sparkling Italian red or white wine" .)