The most common and most likely answer to this crossword clue is the 9 letter word SAILBOARD
I've seen this crossword clue in The Daily Telegraph
S
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More clues leading to the result SAILBOARD
Buddy explains!

The straight part
We know that "something for the windsurfer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case something for the windsurfer = sailboard.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 SAILBOARD mean?
SAILBOARD noun- A recreational device consisting of a surfboard with a small sail on a flexible mast.
- To practice the sport of using a sailboard.