Either a JJill over-the-knee short black, elastic waist skirt (sorry, all three of them I own are well over 10 or 15 years old now, so I cannot share a model # or style #), with black tights, black ballet flats or Arcapedio elastic strap shoes (If I will be doing a lot of walking immediately upon arrival). If going on a more expedition type trip (Artic region, etc.) then I will wear skinny jeans (I like SoftSurroundings Metro Leggings (which come in tall).
Top: a long-sleeve black t-shirt (does not show any on-board spills) and a scarf. A fleece black zip jacket (I used to buy them at Target, but they no longer carry that specific style any more), unless it is the middle of the summer and going somewhere tropical. I always wear a scarf.
First and foremost, as another poster mentioned, is thinking ahead re: what would NOT drag on the airline restroom floor (or any other public restroom floor) and comfort for sleeping on board.....plus ability to then leverage those garments with re-wear on the actual land time.
If I am tight with carry-on luggage space and we are doing an expedition, then I will wear my heaviest, bulkiest shoes on board (I even ALMOST wore artic boots for that reason, and would have changed into regular shoes once on board..but luckily that extreme was not needed...Icelandair was kind..........to avoid checking a bag that could get lost).
Not yet mentioned by other posters: Always a sports bra (to avoid the pain of underwire for 12-15 hours (time counts one or two connections to get to gateway airport).
P.S. If space in my RS carry-on is tight, I have been known to slip my Columbia hooded rain jacket over my light fleece jacket for boarding...ditto for a hat.