The most common and most likely answer to this crossword clue is the 4 plus 4 letter word FAST FOOD
I've seen this crossword clue in The Guardian
F
A
S
T
F
O
O
D
More clues leading to the result FAST FOOD
- Avoid eating fare such as hamburgers, etc
- Escargots presumably not available on such menus?
- Diet of mostly odd junk?
- Son with broken foot tucking into fancy takeaway
- What we eat during Lent?
- What to eat during Lent?
- Burgers, not snails?
- KFC cooking Ramadan menu?
- Rations for the fleet?
- Delivery from rapid server‘s backed-up function, frequently not quite secure
Buddy explains!

The straight part
We know that "Diet of mostly odd junk" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case diet of mostly odd junk = fast food.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 FAST FOOD mean?
FAST FOOD adjective- Of, pertaining to, or serving fast food.