The most common and most likely answer to this crossword clue is the 5 letter word JAMMY
J
A
M
M
Y
Buddy explains!

The straight part
We know that "lucky" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lucky = jammy.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 JAMMY mean?
JAMMY noun- A gun.
- Resembling jam in taste, texture, etc.
- Covered in jam.
- (of a person) Lucky, especially undeservedly so.