It used to be possible to buy ready made B&S - spud, cabbage and onion - which was OK, in fact frying a couple of those was one of the smells that warned my late father that brunch was almost ready ...
Family traditionally made ones - were mashed spud, with maybe added *swede or carrot, chopped up brassica, and *onions (*fry first for extra flavour). Needed a little pepper but no extra salt.