The most common and most likely answer to this crossword clue is the 5 plus 4 letter word HOUSE WINE
I've seen this crossword clue in The Daily Telegraph
H
O
U
S
E
W
I
N
E
Buddy explains!
The straight part
We know that "Drink in bistro, perhaps" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case drink in bistro, perhaps = house wine.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.