The most common and most likely answer to this crossword clue is the 5 letter word MANNA
I've seen this crossword clue in The Times
M
A
N
N
A
More clues leading to the result MANNA
- Article returned by fellow is an unexpected gift
- Heavenly food in fashion, we hear
- Special food not able initially to support fellow
- Spiritual sustenance essential to human nature
- Heavenly food provided by married woman
- Method is reported to produce delicious food
- Emergency rations allegedly made by married woman
- Supposedly wondrous food gives fellow an upset
- Mother taking Ann some heavenly food
Buddy explains!

The straight part
We know that "an unexpected gift" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case an unexpected gift = manna.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 MANNA mean?
MANNA noun- Food miraculously produced for the Israelites in the desert in the book of Exodus.
- (by extension) Any boon which comes into one's hands by good luck.
- The sugary sap of the manna gum tree which oozes out from holes drilled by insects and falls to the ground around the tree.http//www.museum.vic.gov.au/forest/plants/gum.html