He keeps an oily rag in his pocket for quick repairs.
oily rag
idiom Slang
Cockney rhyming slang · East London
fag
Origin
Meaning a cigarette and referring to its soiled state when smokers are employed in a mucky profession.
The mechanic wiped his greasy hands on an oily rag after fixing the engine.
The workshop smelled of gasoline and old metal, with an oily rag discarded carelessly upon the workbench.