The most common and most likely answer to this crossword clue is the 7 letter word VEGGIES
I've seen this crossword clue in The Guardian
V
E
G
G
I
E
S
More clues leading to the result VEGGIES
Buddy explains!

The straight part
We know that "Not these" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not these = veggies.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 VEGGIES mean?
VEGGIES noun- A vegetable.
- A vegetarian.