The most common and most likely answer to this crossword clue is the 13 plus 4 letter word BRING-AND-BUY SALE
B
R
I
N
G
-
A
N
D
-
B
U
Y
S
A
L
E
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.