I have seen a few posts here on r/AskHistorians about the Hundred Years War, such as this question on how the Hundred Years War affected French society or how the Hundred Years War was even able to last that long given population differences between England and France.
However, these questions seem to speak more to the effect of action/fighting.
What was the impact of the sheer amount of time spent on these long wars? Did "ordinary" people outside of combat zones just come to ignore that there really was anything happening, or did they just maybe take for granted that their leaders had "always been at war with the other side"?
(I would also appreciate answers about any "long" war, but my understanding is that there is dispute as to whether other really long "wars" can be considered to be continuous conflicts. As far as I know, even if the Hundred Years is a combination of several different "phases", there was fighting during most of the time period. That's why I included that in the title.)
I can speak about the Hundred Years War specifically. The answer really varies. The Hundred Years War, it must be pointed out, was not really one long war. It was, in fact, three interrelated wars separated by inconclusive peaces. The first between 1337 and 1360, the second between 1369 and 1389 (with a long truce being signed several years after 1389) and a final one between 1415 and 1453. The periods before and between these wars between France and England were marked by other, related conflict conflicts, civil wars like the Wars of the Roses or the Burgundy-Armagnac War, or wars between England and Scotland or between France and Burgundy after the expulsion of the English.
Given that, there is also a lot of range about who, where and when in your question. For instance, people on the Gascon march (southwestern France between Aquitaine and royal France) would have suffered near-constant war damage, routier (irregular, private companies of soldiers) raids and changes of control between France and England. Other parts of France saw a great ebb and flow of war damage and brigandage, with some eastern French regions escaping quite lightly for much of the war. As for England, the war damage was more local. The Scottish march was continually fought over and wasted for much of this period (and long before and after), while Wales saw a prolonged and destructive national insurrection in the first decade of the 15th century. There were also several civil wars in England during the period such as the rebellions against Richard II in the 1380s and in 1399, and the Percy rebellion against Henry IV. So in sum, the war damage could be pervasive and continual, or minimal and infrequent depending on where and when you are talking about.
As for the economic side of things, the 14th and 15th centuries saw the establishment of national taxation systems in France and England. England needed each new grant to be imposed by parliament, while France's government effectively threw off the need for consent as the result of several crises, most notably on between 1356/7 and the late 1360s when the governmnent largely collapsed. Both countries taxed the commoners far more than the clergy (who did grant some taxes) and the nobility, who were usually not taxed directly but did usually have to fight in the wars and were effected by indirect taxes or currency devaluations. These taxes caused several popular revolts over the period that were ultimately put down by the government.
Source: Sumption, The Hundred Years War vol. I-IV. For a more local study, see Vale's English Gascony 1399-1453.
I hope this helps. You might want to make your question a bit mor specific, like "What was life like in London in the early 15th century" or "What would the experience of a Czech townsman been like during the Thirty Years War?"