The most common and most likely answer to this crossword clue is the 6 plus 4 letter word EASTER EGGS
I've seen this crossword clue in The Daily Telegraph
E
A
S
T
E
R
E
G
G
S
More clues leading to the result EASTER EGGS
Buddy explains!
The straight part
We know that "seasonal specialities" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case seasonal specialities = easter eggs.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.