The most common and most likely answer to this crossword clue is the 5 plus 8 letter word PRESS FASTENER
I've seen this crossword clue in The Daily Telegraph
P
R
E
S
S
F
A
S
T
E
N
E
R
Buddy explains!
The straight part
We know that "clip that will to keep things secure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case clip that will to keep things secure = press fastener.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.