I'll be answering mainly from the perspective of England, as its the area whose rural economy in this period I know best (its also probably the best documented too). The key thing to remember is that we can't generalise about "peasants", a term which was, by the way, never used in Medieval England. There was a very complex rural pecking order, based on how much land you owned and what your legal status was (whether you were a freeholder, a villein or a cottager), and so despite a lot of local variation "peasant" society was very unequal, with some peasants being much more prosperous than others. For example at Bishop's Cleeve in Worcestershire, an area with a largely upland pastoral economy where peasant budgets have been reconstructed by Chris Dyer (he's the great expert on late medieval English economic history, and his "standards of living in the later middle ages, 1200 - 1520" sounds like precisely the book for you), an elite peasant yardlander would have a pig to make sausages and bacon, a couple of cows for milk and cheese, thirty sheep to shear for their wool (woollen cloth was in incredibly high demand for local, national and international markets, so it was very lucrative) and draught oxen, while the cottagers (who were far more numerous) would typically own nothing more than a house, a vegetable garden and a solitary cow with grazing rights in the common pasture. Obviously the situation was very different in areas of intensive arable farming i.e. on the Hampshire estates of the Bishop of Winchester, the poorer peasants would typically own no livestock of their own at all, but everywhere the picture seems to be one of inequality. At the same time, this was a dynamic commercialising economy - Bruce Campbell has estimated that between 1086 and 1300 the real supply of coin per capita increased threefold, and everywhere kings and lords were establishing markets, and by 1300 there were 500 - 600 boroughs (towns in possession of an urban charter) in England, almost all of which had regular markets and fairs and so there was nowhere more than 25 km (a day's ride) away from a market. Everyone wanted cash and none more so than lords, who needed it to sustain their households, perform military service and live a genteel lifestyle. A study of 10 lords in South East England around 1300 suggests that they sold just under 50% of the agricultural produce of their demesne lands (lands belonging directly to the lord and cultivated for his profit) on the market. Obviously, a lot of that went to urban markets to feed the growing urban populations, but a lot would also be bought by peasant consumers who went to urban markets to sell their produce, especially since lords preferred rents in cash to rents in kind or labour, and buy what consumer goods they could acquire (French pottery and fine wine have been excavated in peasant households in Wales). As a result of this, what you typically had in many villages by the beginning of the 14th century was a situation in which rich peasants who were more than self-sufficient on their holdings employed their poorer neighbours, who had to mostly live off bought food, as wage labourers - Richard Britnell has estimated that in 1300, wage labour accounted for 20 - 25% of all the labour expended in producing goods (both agricultural and manufactured) in England. So yeah, peasant self-sufficiency in Medieval England is largely a myth and the foundations of what one might call agrarian capitalism were already there in 1300.