The answer to this can be quite specific depending on your location, age and class. Let's assume for the sake of the answer that you're a West Saxon or Mercian peasant, simply because we have far more complete records for those kingdoms in the 9th Century than we do for, say, Northumbria or East Anglia. We'll also assume you're a villein or villager, a tenant farmer holding on average a virgate of land (quarter of a Hide, very, very, very approximately 30 acres), as this was the most populous class of peasantry.

As a tenant farmer, you'd be very surprised to be finding yourself in combat in the 850s, especially if you were in the West Saxon heartlands or in Western Mercia. Until the institution of the fyrd in the 870s, the obligation of military service was extended solely to the thegnly classes, and the Freeman or Sokeman class of peasantry who owned their land outright. This meant that armies were relatively small, but were quite literally elites: contrary to the pop-historical ideas propagated through popular fiction (thanks, GRRM!), a medieval ruler was unlikely to scrape together his untrained peasantry, hand them a sharp stick and point them in the vague direction of the nearest enemy. For starters, it helps to have an army who knows what they're doing and can afford a good standard of equipment; and secondly, conscripting your peasantry can be a good way to destroy your economy and run out of food. As a West Saxon peasant in particular, you'd also be surprised, since Wessex and Mercia had been evolving from an awkward ceasefire towards an increasingly close political, military and economic alliance for close to two decades at this point.

There are, of course, exceptions. It's going to be a bad year for you if you live in or near London, as a major Danish fleet ravaged the city in 850. If you were particularly unlucky, you might have also had to fight or flee against the last Danish raid some 9 years earlier. If, on the other hand, you live in the West Saxon heartlands of Hampshire and Dorset, you've got a fairly peaceful decade ahead until a Danish army attempts to seize Winchester in 860. Things might be different if you were a Freeman peasant who was liable for military service; you may have spent time in the previous decade campaigning in Wales, or periodically marching against the threat of Danish coastal raiders.

The tipping point comes in 871, the year in which Alfred takes the throne of Wessex and the Danish threat to the kingdom escalates rapidly. In that year, the West Saxons fight nine major engagements with the invading Danes, as well as local expeditions against major raiding groups, and "innumerable small skirmishes" against smaller raids. According to Asser, the traditional West Saxon army was "almost annihilated" between the demands of staffing small rural or coastal garrisons or being constantly on the march, meeting the Danes either exhausted or vastly under-strength. Certainly your tenant farmer might have been extremely concerned about armed angry Danes showing up at the door now.

The solution to the West Saxon problem was the creation of the fyrd, a militia organised at shire level who garrisoned the newly-built network of burh fortifications proliferating across Wessex. These were designed specifically to curtail the Danish ability to manoeuvre easily or quickly, and combined with local defensive infrastructure to allow the garrison to respond quickly and strategically to any local threat. The fyrd was a colossal manpower undertaking: burhs typically had a garrison of between 1,200 - 2,400 men, as well as small local garrisons and look-outs to man watching posts and light signal fires along the major roads and rivers. Phrases like "militia" or "peasant levies" have modern connotations which may conjure up a mental image of WWI conscription or GRRM's hapless smallfolk in A Song of Ice and Fire, and you might image your peasant farmer called up and herded into battle, but this was not necessarily the case. The fyrd was simply an extension of military obligation further down the social hierarchy than had previously been the case, to encompass all free men, not just thegns and Freemen. What this meant in effect was that, where a thegn had previously been liable to serve in the gesith of his thegn or the King, he was now called upon to organise a gesith of his own from among his tenants. The fyrd in action was made up of myriad small local warbands, likely recruited at village or 'Hundred' level, which then combined at shire level to form a fighting unit. Military service was a source of some prestige within a community and, providing you survived, could also offer lucrative rewards in spoils, wealth, rank and privilege, and even land. A thegn would fight alongside his gesith in battle, so it was important that the men he chose were capable and dependable. Your peasant may be these things, and be able to equip himself, but of course, he's also at least 20 years older now than when this question started, so he may not be so physically able, depending on his age in 850. That's ok though, as according to the Rectitudines Singularum Personarum there are plenty of other military-peripheral roles he could take. He could, for example, stand turns as a coast guard, man a watch-post or crew a signalling beacon. He could work maintenance on the burghal defences or on the roads and bridges used by the army, or he could simply supply labour on hides devoted to supply the garrison.

Culturally, 'battle' as a concept is likely to have been quite important even if not always present. Society's elite, after all, are a military elite. We know the English were big fans of poetry and song, and epics such as Beowulf, full of heroic deeds of martial prowess, are likely to have been perennial favourites.