lunchbox worn at the waist; low-paid office worker
Historically referred to a lunchbox tied to the waist, then came to mean a poorly paid clerk or office worker who brings a simple lunch. The 'low-paid worker' sense is somewhat dated and often used humorously or self-deprecatingly.
Craftsmen in the old days went to work with a lunchbox hanging from their waist.
He called himself a low-paid office worker and lamented his meager salary.