The most common and most likely answer to this crossword clue is the 9 plus 8 letter word CHRISTMAS PRESENTS
I've seen this crossword clue in The Sunday Telegraph
C
H
R
I
S
T
M
A
S
P
R
E
S
E
N
T
S
Buddy explains!
The straight part
We know that "Things to be unpacked today" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case things to be unpacked today = christmas presents.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.