Comfortable, woven, elastic-waist pants with pockets (I have a flowered pair for spring/summer and a tartan pair for fall/winter). Smartwool knee-high light compression socks in a crazy print that goes with both pants. My bulkiest footwear (usually dad sneakers or Chelsea boots) because, among other things, flying has no guarantees of where I might end up.
On top, I layer, usually 1 more layer than seems necessary. Eg a tank, a buttoned shirt, and a blazer, or T, sweater, and trench.
A big square scarf for multiple purposes.
I travel with a fanny pack for wallet/phone/passport, and use a small backpack as my personal item (with a fabric shopper rolled up inside it)/