The most common and most likely answer to this crossword clue is the 7 letter word DECAMPS
I've seen this crossword clue in The Guardian
D
E
C
A
M
P
S
More clues leading to the result DECAMPS
Buddy explains!

The straight part
We know that "bunks off" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bunks off = decamps.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.
What does DECAMPS mean?
DECAMPS verb- To break up camp and move on.
- To disappear suddenly and secretly.