The most common and most likely answer to this crossword clue is the 5 letter word WHEAT
I've seen this crossword clue in The Guardian
W
H
E
A
T
More clues leading to the result WHEAT
- After tips from Welsh, devour farm product
- Weight trouble? Cereal’s your answer
- Wife’s beginning with warm cereal
- Grass with post-crime police activity
- Wife and husband scoff grain
- Product of farmer’s wife being in season?
- Plant obscured by yellow heather
- Married couple have a diet of cereal
- Grain’s item removed from chicken or veal?
- Corn — that which is full of energy?
Buddy explains!

The straight part
We know that "cereal" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cereal = wheat.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 WHEAT mean?
WHEAT noun- Any of several cereal grains, of the genus Triticum, that yields flour as used in bakery.
- A light brown colour, like that of wheat.
- Wheaten, of a light brown colour, like that of wheat.