The most common and most likely answer to this crossword clue is the 7 letter word FORAGER
I've seen this crossword clue in The Guardian
F
O
R
A
G
E
R
More clues leading to the result FORAGER
- One looking for something for a long time by river
- He searches for another gear
- Pro nurses storm one gathering
- Chapter in Steppenwolf, or a German sustenance seeker
- One seeking food on behalf of a good queen
- Hunter in favour of mature ringleader
- Counterfeit artist engaging a collector in search of food
- Wild consumer on account of long time on end of blower
Buddy explains!

The straight part
We know that "sustenance seeker" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sustenance seeker = forager.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 FORAGER mean?
FORAGER noun- An animal or person who forages