Fish 'n' Chips - little 8p bag of "fish" and "chip" shaped snacks. Bag had faux newsprint on the front. Came in Salt 'n' Vinegar or - yes! - "Mashed potato flavour".
Another pack that has caused much debate over the years are Hedgehog Flavour crisps back in the early 80's From memory they were pork fat in actual flavour ( like pork scratchings without the hairs ) and had a hint of pepper to them.