You'll notice it right away: in Paris the women dress well to go shopping, to go to the cinema, to have a drink; the men look good when they're fixing their cars. Admittedly you may see them wearing sweats now, even when they're not doing something sportif—but we’re not talking gray hoodies. Embroidered designs, quilted materials, animal prints, sparkles: leave it to the French to create a style that’s comfy chic. If you want to blend in, don't wear shorts, traditional sweats, or sneakers. Good food in good settings especially deserves good clothing—not necessarily a suit and tie, but a long-sleeved shirt and pants for him, something nice for her.
Be sure to bring rain gear, a comfortable pair of walking shoes, and a sweater or pashmina for cool churches and museums. You can never tell about the weather, so it's prudent to have a small, foldable umbrella. If you'd like to scrutinize the stained glass in churches, bring a pair of small binoculars. A small package of tissues is always a good idea for the occasional rustic bathroom in cafés, airports, and train stations. An additional note: if you're the kind of person who likes a washcloth in the bathroom, bring your own; they're not something you'll find in Paris hotels.