I thought I'd take advantage of the full-length mirror in my hotel room this weekend to show you the minimum of what I wear to 18th century events.
Here, I've added my under-petticoat (you'd just call it a skirt), a pair of pockets, and a neck handkerchief to fill in the neckline and protect my skin from the sun. For a formal event, my clothes would be nicer, the neckline a tad lower and much more exposed if indoors. The pockets are a separate item, and are not sewn into each petticoat.
I'd then add a shallow-crowned straw hat tipped forward over my forehead a bit, or a black silk bonnet, depending on the weather.
And this is why I get a little cranky when the temperature tops 100 degrees.