The knowledge I have of working people's diets stems from the early modern period, in particular the British Isles, so it sits sort of in the middle of the period in question - around the 1500 and 1600s.Civilian food was not eternally the same, however as meals had to be planned many days in advance, there was certainly some repetition in the diet, however food stuffs were seasonal and necessity of making use of what was available meant meals were not identical all year round.

Cereals
Most of the cereal crops grown in England and Wales during this period were wheat, rye, barley, and oats. These crops had many things in common - they were unusable until ripe, and then they were harvested which usually took place around August. Thereafter the harvested crop was stored still on the sheaf or stalk in bundles in a dry, high place - often the household's loft in order to keep the stored grains as far away from vermin and damp as possible. Of these, most commonly wheat and rye were used for bread although flour could be made from barley or even beans at need.

Contemporaries felt that flour was the most vulnerable state of the process, so very little was kept on hand, meaning that every few weeks the household would have to thresh (beating) a bundle or so of their stored cereals, in order to get the grains ready to take to the mill (after sorting the grains from the chaff - the bits of grass, stalks, and what not. The origin perhaps of "sorting the wheat from the chaff"). The grain would then be taken to the mill to be ground into flour. This is also why mills were often one of the centres of village life at the time, as well as important centres of profit and even some limited taxation.

The process of baking bread as quite long, needing the dough made up about a day before the oven was even fired, which needed about four hours to come up to temperature. Baking bread from flour to load could take as long as 16-24 hours or more, dependent on the amount and efficiencies of the over - all of this needing to be observed and watched carefully.

Barley and some oats could be taken for malting for beer, the most common "safe" drink as water was only trusted when boiled. Oats and some grains such as barley might also be used for the breakfast, soaked in boiled water or even milk if they could get it, for a hearty breakfast.

Peas
June and July were for pulses (peas) of various kinds. Again these could be stored on the vine, dry, and soaked overnight or longer for eating. Some peas were harvested solely for animal food, but in times of shortage or want, could be made into a coarse flour for baking, or boiled into a pease porridge.

June through to September you could hope for some fresh fruit, usually apples or pears, with some stored beyond their season for eating in late autumn, winter.

Nuts were another source of food, with walnuts, hazelnuts, and Chestnuts among those eaten.

Meat
However, meat was a substantial part of the diet (although legally only allowed on Mondays, Tuesdays, Thursdays, and Saturdays), so people would east as much on those days as they could. This would mostly be reasonably fresh beef in the summer and early autumn, some preserved via smoking and salting, but most of the rest of the year the main meat was pork and almost always in the form of bacon or gammon, which was preserved, for eating throughout the year.

Preserved food would usually be initially preserved by cutting, then drying, and then salted. In this manner bacon and fish could be kept for many months. However, to prepare this food for eating would require several days of soaking the preserved meats in water, swapping the water out for fresh periodically in order to remove enough of the salt to make it edible. Many households had a pig, or shared one if poor, which they helped to fatten up and then slaughtered it for the purposes of having meat occasionally over the winter, the poorer the household, the smaller the share of the meat.

Fish, again often preserved, was also a substantial part of the diet, fresh fish less so, as even the wealthy only had fresh fish from local sources, transportation of all food types being difficult.

Dairy
Milk was very rare, except if you owned a cow, the bulk of dairy intake being cheese, which was a large part of a civilians protein intake, and able to last in storage but unlike meat be readily edible straight from stores.

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There were other elements, more rare, which made up the usual diet but those were the main ones. It is not hard to imagine a variety of foods, planned ahead of time, but not monotonous in existence, just regular.

For Further reading see:
Peachey, S., The Soldier's Life in the English Civil War (Stuart Press, 2016)
Morris, R., Medieval Feast Menus 1380-1450 Menus from period cookbooks