Let me start by saying that I am not exactly currently part of a reenactment group. Enthusiasts and authenticity-conscious reenactors may be horrified to know that I was, at one point, part of the Society for Creative Anachronism. Let's be clear. If you like history, want to wear costumes from a bygone era, and would like to be part of a very welcoming group that has very simple (almost non-existant) standards for historical accuracy from a beginner, then the SCA is a great group to which one can belong. I was personally attracted to the words "Creative," (I'm a costumer by trade, and even in college creative was my default adjective for myself) and "Anachronism" (from another time). It's how I met my husband and I made many great friends. If you want to be really authentic, you can; if you want to just have fun, you can do that to. It's purpose is not to exactly replicate the Middle Ages.
If total accuracy is your thing, or an era other than the Middle Ages through the Renaissance, then there are lots of other groups around the world that are much more focused on creating perfect replications of a certain time and place and experience. I have a great deal of respect for the work that goes into this, for the knowledge that the people who do them have, and I am on several listservs with reenactors so that I can learn from them. I am a fringe member of a lovely European group called Lumieres, but living in America means that I can never make it to their events (which are often shared with other groups). I do not want to reenact as an American Colonial, or devote myself entirely to one era. I love history from many time periods and many cultures.
So now that I've put the soap box away; how is reenactment costuming different? Well, for one thing, the focus is on history, education, and accuracy. If your persona would not have had access to the new color "mauve" because she's from a small mining town then you cannot buy it, dye it, or use it in your clothes or accoutrements. If you decide to go ahead and do so then you are knowingly misrepresenting the time period and have basically fallen from clothing into costume. The idea is to lose yourself (and potentially any audience you wish to educate) in the realism of the experience you are re-enacting. A lack of proof that something didn't exist is not a good reason to do it either. You can't prove a negative.
Just how accurate you have to be can be up to a range of people. Just as in theatre the director and producer are the final voice in how the costumes look, so too do some re-enactors have to pass inspection (usually for military units), or just run the gauntlet of gossip. Some people will be harshly critical, and some wouldn't dream of it. In some groups it is entirely a personal choice, but wearing Mary-Janes with your empire dress will probably get you at least a few raised eyebrows, and some polite suggestions as to where you can get better footwear.
Just how far does this accuracy extend? As far as you can imagine. I know of one woman who raised her own sheep so she could spin the wool, weave the cloth, dye it with plants from her garden, cut it with reproduction shears, handsew it with reproduction thread etc, and trimmed it with hand-woven decoration. That's dedication! From time to time I think about trying to do something similar, since I know how to spin wool into thread, but the reality is that I'm both busy and lazy, and that would take a really long time. Most re-enactors try to use fibers and colors that would have been available in their time and place to their persona, and cut their costume according to extant examples, handsewing at the least where the seam will show, and using portraits to determine the kind of reproduction accessories that should go with it. It's like a master's dissertation (and I should know), where you should be prepared to offer a reason for every decision you make. This makes the costume as accurate as possible, and in a roomful of re-enactors it is possible to feel like you've stepped back in time.
Unlike in big-budget movies, re-enacting can be a bit pricey since all of those reproduction items don't come cheap, and no studio exec is paying for them. This can lead to shortcuts. Often newcomers are offered loaner gear by the group they join, with the expectation that in good time they will create their own kit, and the loaner gear can be passed on. Some items like eyeglasses you might not really notice, but others like shoes and hairstyles you will.
The last facet of re-enactment costuming I want to talk about is travel. In film or theater the costumes are either made on site or transported en masse to the location (or very nearby) for the actors to use. In the re-enactment community a social gathering can involve traveling many miles, or even flying. Packing a hoopskirt and a rifle is a lot harder than jeans and a t-shirt.
Unfortunately it's hard to drag a trunk onto a plane.
Fortunately there are ways to lessen the bulk of what you're packing.
For things like hats; you can pack them crown-down on a thin layer of clothes, and stuff the inside with smaller things like stockings, caps, jewelry bags, and gloves. Hoop skirts or panniers can have the boning removed, you'll just have to reinsert it when you arrive. Corsets roll down tightly. Mostly it's about planning how to get the most out of the fewest outfits by mixing and matching strategically. I do this when I pack for long trips in the modern world too. Solids colors that compliment each other and a few key pieces will go a long way, and limit yourself to two kinds of shoes if not one.
Are you a re-enactor? Want to add something? Have a question? Leave a comment!