The most common and most likely answer to this crossword clue is the 7 letter word GRISTLE
I've seen this crossword clue in Financial Times
G
R
I
S
T
L
E
Buddy explains!
The straight part
We know that "What’s left on the plate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what’s left on the plate = gristle.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 GRISTLE mean?
GRISTLE noun- Cartilage; now especially: cartilage present, as a tough substance, in meat.
- (from obsolete scientific theory) Bone not yet hardened by age and hard work.