First of, most battles weren't conducted in people's fields. Most land wasn't owned by a single person, but rather in common use by the community to graze or herd animals, for example. Wild, untamed nature was a common thing, with large, dense forested areas and unworked fields between settlements. You can add to this that most armies fed themselves of the lands they marched through, so they would leave the whole region stripped of all its food and resources.

But let's say they fought in your field.

I hope you fled when you had the chance. Armies of thousands aren't going to simply meet in your field, they will fight their way through your village, or reduce every hiding spot (your buildings) to ashes. If you had animals they would have been slaughtered, any food you had stockpiled would be gone.

I hope your fields needed to be plowed, because they will be. Depending on the type of conflict, looted corpses of men and horses would be spread about, or your field may have been repurposed as a mass grave (if they buried them deep enough this might not even be a real problem for you, at least not this year).

I would caution you against returning to your village immediately, though. Roving bands of armed men and campfollowers will take whatever they can get, at least for the next week.

In summary: you have no harvest, no stockpile, no animals, no buildings. Good luck surviving on that. Your local lord might still require you to pay your taxes or rents, though.

Big, long-lasting conflicts severely disrupted or outright destroyed local economies and would result in a 'scorched earth' that could be used to starve out enemy armies (if your army didn't starve first). Armies usually weren't supplied by their leaders or country, but lived of the land. The men weren't the disciplined soldiers we think of today, and many men deserted one army to terrorise the locals, until they were (forcibly) snapped up by another army.

When gunpowder made its first entrance very little changed. Canons were used in sieges, to damage a cities or castles defences, but this didn't change the way armies and wars worked for the common folk. Its only when guns become more reliable that armies adapt to utilise them. Reloading takes time and requires practice, so men need to be trained to do this. Once you start training your men, you can teach them certain tactics, which require discipline. These trainings also require a large investment of time and energy on the part of the soldier, who is not only becoming more disciplined, but also more loyal to the people around them (regiment) or even the novel idea of a nation/state/country/king. This all results in a gradual formalisation of armies and war (simultaneously, more centralised states emerge). Supply lines are still not reliable, though, so our farmer's descendants still pray for the army to stay away.