I dress for comfort and my destination. If it's an overnight flight to Paris or London, my uniform is much like Angie's: straight-legged jeans with some stretch, a T/camisole with a light jumper, a jacket or raincoat, low-heeled boots or shoes, and a scarf. I like to wear something that feels comfortable enough to sleep in during the flight, but still looks presentable when I'm on the ground the next day, especially if I won't be heading straight to a the hotel. I find it easier to cope with jet lag if I stay active until 8 or 9 pm in my new time zone.
A couple of tips:
Because I hate walking around a grubby airport in my socks, I slip on a pair of foldable, ballerina-style slippers just before security and carry my boots through. I also remove any jewelry or metal items before the line-up so I can go through the scanners without problems.
I travel with only two items in my hands--my small carry-on and my Longchamp Le Pliage tote. I find this more efficient for going through security and for navigating unfamiliar airports, and local transit, on my arrival.
My cross-body travel handbag contains my passport, money, and credit card and it is tucked into my Longchamp tote during the plane trip. The tote also contains my scarf, iPad, headset, snacks, folding umbrella, and jacket/raincoat (folded in a large ziplock). On an overnight flight, I also throw in a pair of my husband's old socks to wear over my regular socks so I can walk around the plane without my shoes, a baby-sized pillowcase that I can stuff with my jacket or sweater, and a mini toiletry kit so I can freshen up before landing. The tote sits under the seat in front of me so I can get at everything easily without having to access my carry on during the flight. Having only two items means I don't have to worry about leaving something behind and I can easily move around when I arrive. If I know I can't check in to my room for a few hours, I can stop in a cafe for a quick lunch or a drink with just these two items.
Contrary to some of the others, I find that airplanes temps can range from boiling hot to freezing, so I always dress in layers. If the plane is overly warm, I can strip down to my T-shirt; if it's freezing, I wear my sweater, scarf, and even my jacket.
My travel "uniform" also works if I'm going from a cold climate to a warmer one. Depending on where I'm going, I can quickly change my shoes for sandals, or my jeans for a skirt, once I've arrived. In this case, I'd probably just make sure that the items I want are right at the top of my carry-on so I can find them quickly. My Longchamp tote becomes my shopping tote at my destination since I usually use my cross-body handbag at my destination. I do remove my passport, credit cards, and ID from my handbag, though, and put them into a waistband pouch that I wear under my clothes for the duration of my trip. I've seen handbags grabbed from unsuspecting travellers so I'm quite cautious about what I keep in my handbag.
