The most common and most likely answer to this crossword clue is the 7 letter word NOUGHTS
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More clues leading to the result NOUGHTS
Buddy explains!

The straight part
We know that "casual additions to fat cats’ bonuses" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case casual additions to fat cats’ bonuses = noughts.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 NOUGHTS mean?
NOUGHTS noun- Nothing; something which does not exist.
- A thing or person of no worth or value; nil.
- Not any quantity of number; zero; the score of no points in a game.
- The figure or character representing, or having the shape of, zero.
- To abase, to set at nought.