The most common and most likely answer to this crossword clue is the 6 letter word BARIUM
I've seen this crossword clue in Financial Times
B
A
R
I
U
M
Buddy explains!

The straight part
We know that "Elementary meal prepared to give inside information" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case elementary meal prepared to give inside information = barium.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 BARIUM mean?
BARIUM noun- The chemical element (symbol Ba) with an atomic number of 56. It is a soft, reactive, silvery alkaline earth metal.
- A single atom of this element.
- Barium sulfate suspension.