The most common and most likely answer to this crossword clue is the 11 letter word LEISUREWEAR
I've seen this crossword clue in The Times
L
E
I
S
U
R
E
W
E
A
R
Buddy explains!
The straight part
We know that "things to don in spare time" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case things to don in spare time = leisurewear.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 LEISUREWEAR mean?
LEISUREWEAR noun- Clothing worn for leisure or as general casual wear.