The most common and most likely answer to this crossword clue is the 9 letter word RUCKSACKS
I've seen this crossword clue in The Daily Telegraph
R
U
C
K
S
A
C
K
S
Buddy explains!
The straight part
We know that "when loaded often they get worn at the rear" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case when loaded often they get worn at the rear = rucksacks.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 RUCKSACKS mean?
RUCKSACKS noun- A bag carried on the back or shoulder, supported by straps