A writer has one real problem after reading a lot of history.
He can't assume that the past is like the present.
It may take some time to acquire the habit, but soon, writing merrily along on a scene may abruptly end as the writer realizes that the scene is outside, at night, and no light source has been specified.
Sometimes this works out just fine. Realizing that while beacons can convey single concepts such as "we are under attack", and church bells can cover perhaps half a dozen, from "alarm" to "service" to "someone died", the speed of communication for any marginally complex concept is the speed of a horseman, and how often he can change horses. As a side effect, this allows the man on the spot, such as your character, a lot freer hand than we would expect with modern communications.
Other issues can be elided, because what would strike the modern reader is commonplace and unnoticed to the point-of-view character. Dirt would simply be taken for granted, not fussed over.
On the other hand, many differences are so plot-significant they can not be missed. The flip side of the communications is that the character may not be able to communicate with the locals. At the time of the French Revolution, most inhabitants of France did not speak French but a local patois. Despite the way a lingua franca emerges on travel routes, getting off the beaten track would make communication impossible, and even on the routes, you had to find translators often enough. In a realistic D&D setting, "Comprehend Languages" would easily be more valuable to a traveling party than "Cure Light Wounds."
Not that Cure Light Wounds would not be vital. Medieval and even early modern mortality rates were sky-high, and anyone could and did die at any stage of life. Even among royalty. King Aethelwulf had five legitimate sons, and the youngest succeeded to the throne, after all four of his elder brothers died without issue (though three lived to succeed to the throne in their own right). Queen Anne, despite numerous pregnancies, had more stillbirths and miscarriages than live births, and one child lived to the age of eleven. The transition is perhaps more sharply delineated in royalty than it deserves. King William IV had no legitimate children who lived to grow up, and so his niece became Queen Victoria. Queen Victoria had nine legitimate children who all lived to grow up, which was thought little short of a miracle.
This is perhaps less surprising when you consider that the finest castle of two centuries would be illegal nowadays, deemed "unfit for human habitation."
Those with less would fare worse. This is just part of life at the time. Not a pleasant part, grief for young children is recorded in all sorts of literature, but if your intrepid band arrives at an inn where the inn-keeper and his wife have an eleven-year-old, a seven-year-old, and a year-old baby, all the characters will take for granted that the nine-year-old, five-year-old, and three-year-old almost certainly died. (Babies coming two years apart being the general rule.)
Not to mention less than fatal problems. Despite more than ninety percent of the population being engaged in food production, famines were a chronic problem, and malnourishment was the rule, not the exception. It would stunt growth, make them less intelligent, weaken their immune systems, and otherwise harm them. Peasants should be shorter than kings for not eating so well growing up.
Warmth was another constant problem. Clothes were worn until they were worn out, and then cut up to use as patches to make other clothes last longer. (Even if this entailed their passing from hand to hand, generally down the economic ladder.) The clothes of the dead were used even if the death stemmed from disease; this was a major issue in transmission up to the 20th century even in the most industrialized countries. Fire was another constant problem. One reason that Chinese cuisine consists of such finely chopped foods is that by chopping them so finely, you minimize the amount of wood you need for the fire. Places where there was less arable land fared better for firewood, but it inevitably grew short. In London, the normal means of heating a home and cooking a meal was coal by the reign of Elizabeth I.
Then, coal or wood, you want to keep the fire burning, even if banked, for all the cost of fuel, because there's all the difficulty of starting a fire. There were early modern tools bought solely to bear coals from a neighbor's fire to light your own.
Light was likewise hard to obtain. The vast majority of work was done by sunlight -- moonlight if available -- and sometimes by starlight, which does shine brightly enough to walk by. Candles are ferociously expensive for the vast majority of the population, and firelight is often too dim to work by. Which meant it contributed to accidents. And since all artificial lighting was by flame, it contributed to fires, which could not only kill directly but wipe out a family so they starved.
The way this hardship was kept from wiping out the human race was babies. Many babies. The average woman spent her childbearing years either pregnant or nursing, if she lived through them. (Wet nurses were, of course, luxuries for the rich and contributed to infant mortality because the rich hired only the mothers of newborns and expected them to nurse the rich newborn instead of their own.) This greatly limited activities she was capable of.
Travelers had problems. Roads were habitually terrible. Despite the vastly greater amounts that a draft animal can pull on a cart rather than carry, many travelers used pack animals because the roads were impassible by cart. Crossroads have a reputation as dangerous, liminal places, because they are places where you could take a wrong turn, which could be anything from a setback to a lethal danger. The sea, or rivers, were much better for travel, but the seas were at the whims of winds, and rivers were often subject to tolls by every lord who could block the way.
And then when you got there -- the lack of communication, the difficulties in reading any credentials you care, the wariness toward strangers, meant great difficulties. A merchant with a regular route, or joining with others who had such a route, perhaps had the least difficulties. But a stranger without such an excuse or familiarity from past visits would meet with vastly more distrust than nowadays. Lacking connections by blood or marriage or even association, travelers find it difficult to find even knowledge, let alone employment. The locals jeer off even truthful complaints of serious crime, if they don't claim you are the criminal, in your own case or someone else's. And with the justice system as crude as it is, evidence is hard to come by and organize. Criminals who flee will simply escape because there is no organized hunting of them once they get past jurisdiction. Locals do have some reason to mistrust, therefore. If you left somewhere where you had connections to come here, escaping criminal charges is a good reason, and there aren't many others.
This is far from exhaustive. These are merely a grab bag of such issues as I remember off-hand.
It's also why I prefer to write high fantasy. An essay on how to alleviate such problems may be forth-coming.
This is a good list of things to remember for a fantasy story. It also makes me wonder how it'd work with a reversal of the usual story idea of people from modern (or near-modern, like say, WW2) earth ending up in a fantasy land. What if a person from the fantastic realm ends up in modern days instead? What if Mister Tumnus or Trumpkin the dwarf had found their way to WW2 England? It'd be interesting to see how such a person would react to a society that didn't have to deal with all the problems you listed above.