Islanders endlessly paid to fill preserve containers (9)
I believe the answer is:
jamaicans
'islanders' is the definition.
(I have seen 'Caribbean islanders' mean 'jamaicans' so perhaps 'islanders' could also mean 'jamaicans')
'endlessly paid to fill preserve containers' is the wordplay.
'endlessly' means to look at the middle letters (the ends of the words are removed).
'to fill' indicates putting letters inside.
'preserve' becomes 'jam' (jam is a kind of preserve**).
'containers' becomes 'cans' (can is a kind of container).
The middle of 'paid' is 'ai'.
'jam'+'cans'='jamcans'
'ai' placed within 'jamcans' is 'JAMAICANS'.
(Other definitions for jamaicans that I've seen before include "West Indians" , "Caribbean islanders" .)