The most common and most likely answer to this crossword clue is the 7 letter word TUCKBOX
I've seen this crossword clue in The Times
T
U
C
K
B
O
X
Buddy explains!
The straight part
We know that "what Bunter was always going to?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what bunter was always going to? = tuckbox.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.