I’m reading about the English longbowmen of the Hundred Years War and the wealth that they earned through chevauchees in France. If he is first a farmer by trade, what could he spend this extra money on if social classes are rigid? I doubt a common soldier would gain enough wealth to become a landlord, so how exactly would extra wealth help him, aside from making his life more comfortable.
England at the time counted three separate social classes: the nobility, the gentry and the peasantry. Yeomen originally belonged to the peasantry but climbed up the social ladder by acquiring lands and stock so that they constituted a 'middle-class' between the peasantry and the gentry. Their fortune, however, generally didn't last more than two generations.
During the Hundred Years' War, agriculture was a poor investment. The labour costs were high and the benefits almost non-existant. Despite their increasing wealth, yeomen lacked the capital to make their fortune last. Therefore they also often spent it to further their personal status and ambition rather than to consolidate their family's subsistence--they purchased masses for their souls among other things.
They largely invested in their own houses and set new norms of comfort all accross the country. Yeomen were able to build private rooms, buy silverware and make their houses a cosy place to eat, rest and even entertain friends. They also bought new furniture and more expensive clothes. As far as personal freedom and lifestyle go, the peasantry underwent a "golden age" during the 15th century despite the recurring plague, the increasing taxes and the aggravating wars.
Beyond spiritual and material goods, yeomen also bought military hardware: longbows, arrows, armor, horses... By the 14th century already, yew for longbows was imported from Poland through Teutonic Prussia. Longbows and fletched arrows became increasingly expensive. Yeomen's military equipment value defined their social status within the military. They had to buy better hardware to make it to the Royal Guard. Getting closer to the king also meant they were entitled to a larger booty upon seizing a city or claiming a victory on the battlefield.
Yeomen were faced with different possibilities when spending their new wealth: land and stock? a more comfortable house? spiritual guarantees for their soul? a better military equipment? Nevertheless, the money didn't last far beyond their gravestone. In the meantime, he rose above the common peasantry and fashioned his lifestyle on the gentry.
Cf. Gerald Harris, Shaping the Nation (2005); Matthew Strickland & Robert Hardy, The Great Warbow (2011, reprint).