Being compatible with drink, supply can in advance (7,2)

'being' is the definition.
The answer and definition can be both to do with fundamental existence as well as being present participle verbs.
Perhaps there's an association between them I don't understand?

'compatible with drink supply can in advance' is the wordplay.
I cannot really understand how this works, but
'drink' could be 'gin' (gin is a kind of drink) and 'gin' is present in the answer.
'supply' could be 'fit' (fitting is a kind of supplying) and 'fit' is present in the answer.
'can' could be 'tin' (both are metal containers) and 'tin' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?