You know to look around the Internet, but there are otherr places where information is waiting for you.
Microfilm and Microfiche
To begin with, you can get a catalog of periodicals and other publications on microfilm from the folks in Ann Arbor who supply the library. Ask the librarians to let you look at their copy first, but if it covers your era, you'll want your own to mark up. If you don't have room in the apartment for your own microfilm reader (about twice what a decent video game machine runs, nowhere near computer costs), buy your films and microfiches, then take them to the library's machines.
Magazines like the Spectator began in the 18th century, and many newspapers are available to their earliest copies. Don't guess what the weather was like in London that day in 1793, find out (though not one in a million readers could contradict you). More reasonably, you can find out what was in the news, how many ships came and went from where with what cargos, what prices ran, who was throwing parties, if no-one was throwing parties because it's grouse season and everyone is off in the country, etc. Catalogs
The periodicals-on-microfilm catalog itself tells you what periodicals are available for your character to buy, thumb through, or knock on the floor. Some have had gaps in their publishing history. More importantly, how far back were ladies consulting Godey's, or men the Police Gazette? Do look out for editorial policy changes. Cosmopolitan was not always a fashion magazine. Argosy the men's magazine began as the family fiction magazine, Golden Argosy.
Reproductions of period catalogs are available, from Bloomingdale's to Sears, not excluding Montgomery Ward's and various smaller companies, for Victorian plumbing supplies, wicker furniture, and carriages. The Dover Publications catalog lists many. These allow you often to assess prices for the period, as well as determine what tools were available, what the fashion buzzwords were, what were the common clothing colors, and a host of other details for the common rather than wealthy person.
Modern catalogs may help you out. If you've read names of Victorian fashion items but have no idea what the doodad looked like, Amazon Dry Goods, which supplies re-enactors, may have pictures of the reproduction of the item, besides lots of books for sale. In black powder gear, Dixie Gun Works sells parts and accessories (far fewer arms than in their heyday), all sorts of clothes and possibles, well illustrated, and a tremendous selection of books on mountain men, free trappers, and militaria.
Stepping back or away farther, Museum Replicas and its parent company, Atlanta Cutlery, show clear pictures of a wide variety of bladed weapons, from the latest Gil Hibbens show knives to working-pipe tomahawks to authentic Medieval and Dark Ages blades, from daisho to kukris, with weights, descriptions, often fairly precise dates.
Replica Gear
Having these re-enactor catalogs in hand, you may be wondering how much this gear is like the originals. Would it help your writing to actually swing a rapier or a broadsword, put on a barbute or a farthingale, see how much space it takes to hide a dagger or pilum?
In most cases, yes, if you allow for the differences in size and background between yourself and your characters. What is unwieldy to a 5'6" author may be handy to a six-footer like the character is supposed to be. What is uncomfortable to soft palms that spend their lives keying in stories may be unnoticed by range-hardened hands. The cure here is to get a friend closer to the character in characteristics to try out the gear. This includes male authors having a woman try out the corsets and hoops.
Unless you simply want to repeat everyone else's descriptions, some things you should try to experience for yourself. This includes shooting firearms or crossbows your characters use, since they are relatively easy to learn. For example, black powder pistols do not kick like smokeless ones; you cannot take your experience with one and transfer it to the other.
If you don't know archery already, you are best off watching and listening to archers at the butts, and perhaps learning how to draw a simple bow. The problem here is that since the Seventies, the pulley bow has taken over to such an extent that many archers are ignorant of traditional practice and language. For example, they call their pulley bows "compound bows" a term traditionally used for any laminated stave, whether fibreglass and wood or horn and sinew. Of course, pulley bows don't feel or sound too much like stave bows, notably because of the built-in let-off, cutaway sight-window, and formed grip. The ones that are teched up with multiple layers of pin-sights and peep-sights, mercury stabilizers, etc., are completely divorced from a bare, tapered stave of yew with a leather grip around the middle.
Choose your sources carefully, or the gear won't be authentic, and may therefore mislead you. Hank Reinhardt of Museum Replicas does not sell pot-metal "decorator pieces," but "battle-ready" authentic blades. They feel, handle, smell, and sound as much like the originals as possible. Their only drawback may be being made of steel so fine that they would have been "magic swords" back then. Some of us remember Hank for very realistic S&S fiction, editing good anthologies, and some background articles on armour and weapons in Heroic Fantasy from Ballantine. On the other hand, Collector's Armory sells excellent replica, non-firing firearms, so you can see how they weigh, handle, hide, cock, draw, and often break down, but their swords are mostly the decorator junk you find at import shops, overweight and soft. Be wary of any of those coming from Spain, marked "El Cid" and the like. They are strictly wall sculpture.
As well, you may want to try out costumes, but do remember that you will often be wearing it in 20th century architecture, designed for minimalist clothing, not hoops, houppelades, hennins, rapiers, poulaines or busbies. Try to find someplace spacious at a school, church, theatre, or social hall, in which to try walking and turning. A fifteen by twenty front room with furniture is barely room to get dressed, and our ordinary eight-foot ceiling would have been only found in those "low-ceilinged" smoky taverns.
Note that you can't judge some things without training. A hoopskirt is damned impossible until someone teaches you how to handle it through doors, and shows you how to sit without having it sproing up in your face and reveal to all the world what it is supposed to conceal.
In short, actually using replica gear may reveal immediacies of experience mere observers miss. You may find that the episodes of derring-do that you have read dozens of times simply aren't very possible with the weapons or shoes of the time. However, you had better be already so deep in research that you can determine what is authentic or not, and so that you can use the items in the proper way. Otherwise, it is too easy to dismiss stuff as foolish, clumsy, and ineffective because it does not suit modern experience and practices, as in many authors' disdain for sidesaddles.
Period Food
Don't say anything bad about the food until you've tried it. Yes, a lot of you never eat anything you haven't eaten since you were seven. In that case, don't run down the food of other times and places just because it isn't your food, anymore than you should call foreign food "inedible." No whole culture ever lived regularly on a diet they didn't enjoy eating, at least not until the 20th century invented diet doctors.
We were once really irritated at an otherwise excellent novel that ruined its credibility with us by describing eels in honey as slimey black chunks. Excuse us, but while a live eel is slimey and black, a live chicken is a none-too-appetizing mouthful of feathers, quite different from good fried chicken. Eel meat is white and tasty, popular in many parts of the world, from England to Japan.
So if you ever mention food -- and it is awfully artificial not to -- find a good book of modernized period recipes and try it first. One writer was extremely surprised to find that the much-maligned Spartan diet was light, simple, tasty, and nutritious, while the multi-course Athenian banquet with sauces made with myrhh, rue, asafoetida, and the like, was nearly insupportable to the modern American palate. It completely changed her descriptions, especially since Greek olives look as well as taste rather differently than the ones packed in California, even when they are called Calamata or Greek-style.
If your diet does not permit, or you always hate strange food, just be guided by the period authors. If they love silphion, a bitter asafoetida-like herb, or gobs of horseradish, your characters probably ought to, no matter that you couldn't choke it down.
Sewing Patterns
We don't mean Simplicity, Butterick and McCalls. Their Halloween costumes are a long, long way from authentic. Don't even look at them.
On the other hand, both Dixie and Amazon offer a wide variety of authentic patterns: Amazon has a whole separate catalog for patterns alone. For clothing information on the Middle Ages, you can do far worse than to consult Patterns from the Past, even in place of many books. They give a lot of detail on fabrics, patterns, trims, and accessories.
This particular company also has a package of tent designs, for SCA'ers wanting to build pavilions, which will tell you more about portable shelter before 1900 than any book we've seen. Much of it derives from Viollet-le-Duc, as one can tell from the excellent, authentic designs offered.
Static Plastic Models
One writer of our acquaintance, working on an action-adventure novel, bought a European-made model of a certain plane (he'll kill us if we give away too much detail) just so he could get more familiar with the lines and structure of it. In the background paragraphs on the assembly sheet inside, he found out about an adaptation of the plane that was not mentioned in any of a dozen books he had read, that gave him an entire plot element (thus the paranoia, until the manuscript sells).
An historical novel can be defined as one in a period you didn't live through as an adolescent or adult, so that you have to research it and reconstruct it. For many of us, the Sixties, even the Seventies count as an historical period.
The cars of a period can be vitally important: before 1980, you are what you drive. At the same time, you may have many readers who owned or own the rotten thing, and will say evil about you and your research if you have it in the wrong factory colour or the ashtray in the wrong place. Building a plastic static model of the car is the next best thing to sitting in one. You can literally check on blind spots, underseat stashes (in scale), and learn about engines and suspension.
On the other hand, you can also find models of 19th century cars, and are they another world! Of course, if you are doing WW2 or The Great War, you should look into planes and tanks of the time. By the time you finish building a Nieuport, you will be far more familiar with it than when you were only looking at pictures.
In Sum
As you can see, as an historical novelist, you should keep your eyes open and check out anything associated with your period that has the least claim to authenticity. Play with the toys -- cook food, build models, wear funny clothes -- it's educational.