The most common and most likely answer to this crossword clue is the 4 plus 4 letter word ROCK SALT
I've seen this crossword clue in The Guardian
R
O
C
K
S
A
L
T
More clues leading to the result ROCK SALT
- Rubbish contains various bits of slack mineral
- Mythical bird talks outrageously, coarse stuff
- Seasoning sailor from Gibraltar?
- Way to get last mineral
- Addition to food staggers a junior officer
- Culinary requirement of a sailor from Gibraltar?
- Repaired last underlying crack caused by de-icer
- Last cooking ingredient
- Make last possible contents of cellar?
- Enormous bird sets task back carrying large edible crystal
Buddy explains!
The straight part
We know that "possible contents of cellar?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case possible contents of cellar? = rock salt.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.