The most common and most likely answer to this crossword clue is the 5 plus 3 plus 3 plus 4 letter word BRING AND BUY SALE
I've seen this crossword clue in The Daily Telegraph
B
R
I
N
G
A
N
D
B
U
Y
S
A
L
E
More clues leading to the result BRING AND BUY SALE
Buddy explains!

The straight part
We know that "charity event" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case charity event = bring and buy sale.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.