Following on from the recent baguette question (what if the bread kneaders hands were dirty?) French fries cooked in a wire basket in a vat of vegetable oil used only for that purpose.
In a diner with non kosher ingredients, are the main obstacles here: the knife that cut the spuds, and the plate they are served on? If they give me a paper plate... then just the knife? If they tell me it is a single-purpose knife.