The 'slang' name given to being a shelf stacker / general dogs body at Sainsburys / Tesco and so on.
The role used to include (and may still, as a breach of health & safety) having to collapse the cardboard packaging & literally climb into the large bin containers to compact it down!
See also 'McJob' for other equally shite low IQ jobs.
"So what's your job then?"
"I stack shelves at Somerfields"
"Oh, so you're a shit boy then!"