The most common and most likely answer to this crossword clue is the 8 letter word BOATLOAD
I've seen this crossword clue in The Times
B
O
A
T
L
O
A
D
More clues leading to the result BOATLOAD
Buddy explains!

The straight part
We know that "cargo" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cargo = boatload.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 BOATLOAD mean?
BOATLOAD noun- Cargo or passengers that fill a boat.
- A large quantity.