I can answer some of these questions in relation to the Anglo-Saxons. In early medieval England, the vast majority of the economy was agrarian, with the crops and land use varying wildly by area. Land in charters is often measured in a bewildering variety of measurements - sulungs, manetes, cassati - but in terms of productivity was often assessed in 'hides'. By the late ninth and tenth centuries, land in each shire was measured in hides, with a portion assigned to each burh to provide for the garrison. Depending on the soil and the crop, a 'hide' could vary greatly in size. In East Anglia or Kent, for example, fertile soil for crops meant that hides could be much smaller than those in the rugged scrublands of the West Midlands where the primary activity was sheep and cattle farming. A 'hide', roughly, is about enough land to support its tenants for the year. In Wiltshire, as an example, 2,400 hides were designated to provide for the garrison of Winchester, who wouldn't be able to tend their own crops while on duty. The assessment of land in productive hides can be seen most clearly in the Domesday Book.

Excavations like those carried out at Stafford by Carver et al in the 1970s show some insight into the diet. Cattle and sheep were both processed in vast numbers at the site, as well as a wide array of game birds. Staple crops included oats, wheat and barley, all of which were used to produce bread loaves or 'bannocks'.

The agricultural year was tightly regimented. The medieval Church held astronomy in high regard, and kept very accurate calendars, in part to accurately calculate the dates of Easter. Surviving specimens at the British Museum show us that these were often illustrated with scenes to show what the farming population should be busying itself with in any given month. These are part of a wider trend of "labours of the months" iconography common to early medieval calendars across Europe.

In January, for example, farmers should be repairing tools or buildings, weaving baskets or planting. In February they should be ploughing and fertilising their fields. Spring time spent not tending livestock could be spent weeding and pruning crops and keeping foraging animals away, until summer crops can be harvested in July, the fields reploughed, and winter crops planted, with other crops harvested in August and September. By Autumn, farmers might be miling their grain, butchering their animals and preparing the meat, sowing seeds, weaving storage baskets or repairing buildings in preparation for the winter. Other activities included hunting, feasting, threshing and foraging for acorns, nuts, berries and fruits.

You can read more about the Labours of the Months here. This is a fine 19th century version of the same. I'd also recommend Time in the Medieval World - Occupations of the Months and Signs of the Zodiac.