The two staple foods of peasants and townsfolk were porridge and brewet. Brewet was a meat dish, by definition, but both kinds of food could have just about anything in them. (Sort of like the modern word “casserole”)
Porridge began with any kind of seed that could be coarsely ground or crushed. It could use grains like wheat, rye, barley, millet or buckwheat (which is technically a grass seed). It could also use nuts, such as chestnuts (and probably any other kind of nut, like acorns if the pigs hadn’t eaten them all); it could also use dried peas. Porridge was just boiled until soft and thick. Where possible, it was seasoned with salt. Also where possible, it was boiled with milk, not just water.
Peasants expected to eat twice a day, and porridge was always the main dish of one meal, often both. Making bread entailed either owning a lidded baking pot and enough fuel to create hot coals, or having enough grain to spare that it was all right for the village baker to pinch off 1/5 of the dough you brought in. Also, even the worst bread required enough grainy matter to make a loaf. Porridge, on the other hand, could be made with just about anything, in just about any kind of pot.
Townsfolk ate porridge too, but they could expect their second meal to include some meat. Brewet was meat stew in a cream sauce. The meat could be any sort: pork, hare, chicken, or mutton. To be brewet, it had to be in a seasoned cream sauce. Town people could afford salt and local herbs like chives or leeks. By the late Middle Ages, they could afford pepper.
Our recipes for brewet are all from professional cooks who had a variety of materials unknown to others, from almonds to roast boar. Brewet on castle tables used colored, spiced sauces. It never included vegetables. That doesn’t mean that ordinary people in town didn’t put beets, onions or carrots into their brewet. It seems likely that they ate what they could get, and that professional cooks left vegetables out partly because they didn’t see any reason to provide instructions for them and partly because vegetables were the food of the poor. This leads us back to the likelihood that an ordinary citizen’s supper brewet had cabbage and beets.