The most common and most likely answer to this crossword clue is the 9 letter word GIMCRACKS
I've seen this crossword clue in The Daily Telegraph
G
I
M
C
R
A
C
K
S
Buddy explains!

The straight part
We know that "Useless stuff" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case useless stuff = gimcracks.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 GIMCRACKS mean?
GIMCRACKS noun- Something showy but worthless; a gimmick or bauble.
- To put together quickly and without much care; to bodge.
- To embellish with gimcracks.