The most common and most likely answer to this crossword clue is the 11 letter word PORTMANTEAU
I've seen this crossword clue in Independent
P
O
R
T
M
A
N
T
E
A
U
More clues leading to the result PORTMANTEAU
- City rivals swallowing drink after drink in case
- Alcoholic drink and non-alcoholic drink consumed by soccer team in the case
- Case left by chap having meal with union leader
- Left chap kind of cross about English classification of the across solutions?
- Drink, mister and, it’s said, pull a bag
- Hague regularly pursuing Oscar-winning actress, one half of team Brangelina?
- Left chap note with a uniform in case
- Dock on isle and cross round base in carrier
- Harbour staff reported tug in case that’s needed on voyage?
- Trunk left on board by ship’s officer, containing new gold
Buddy explains!

The straight part
We know that "case" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case case = portmanteau.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 PORTMANTEAU mean?
PORTMANTEAU noun- A large travelling case usually made of leather, and opening into two equal sections.
- A schoolbag.
- A hook on which to hang clothing.
- A portmanteau word.
- To make a portmanteau word.
- Made by combining two (or more) words, stories, etc., in the manner of a linguistic portmanteau.