What does the cryptic crossword clue "Basic foods keep (5-3-6)" mean?

The definition is "keep". The wordplay uses a double definition. Double definition The answer is Bread-and-butter.

What is the answer to "Basic foods keep (5-3-6)"?

The answer is Bread-and-butter.

Telegraph Prize Cryptic #3092 | 20 Across | 2021-01-24 flower