Plural of crummy; multiple poor-quality things, or informal clothing (British dialect).
From 'crummy' in both its adjectival uses; as a noun it can refer to shabby items or in mining/nautical dialect, work clothes or undergarments that get dirty and crumbly.
In British mining and nautical communities, 'crummies' were the work clothes you'd change into—they'd get covered in crumbs of coal dust and dirt, so the name literally matched their condition!
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