The most common and most likely answer to this crossword clue is the 2 letter word BU
B
U
Buddy explains!

The straight part
We know that "Overstuffed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case overstuffed = bu.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.
Crossword Answer definitions
BU noun- A dry measure, containing four pecks, eight gallons, or thirty-two quarts.
- A vessel of the capacity of a bushel, used in measuring; a bushel measure.
- A quantity that fills a bushel measure.
- A large indefinite quantity.
- The iron lining in the nave of a wheel.