The most common and most likely answer to this crossword clue is the 5 plus 5 letter word BLING BLING
I've seen this crossword clue in The Guardian
B
L
I
N
G
B
L
I
N
G
Buddy explains!
The straight part
We know that "Flashy stuff" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case flashy stuff = bling bling.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 BLING BLING mean?
BLING BLING noun- Shiny jewelry that displays wealth, such as a diamond ring or a stylish gold necklace or bracelet.