Coat, Columbia | Sweater, thrifted | Pants, Old Navy | Boots, Bogs | Scarf, gift (Kohl's) | Backpack, Herschel Supply Co.
4. Use a backpack as a personal item
As long as your second, smaller carry-on fits under the seats, you should be good to go. The space has been surprisingly deep, and I've been able to bring both my violin and stuffed Herschel on board with no problem. Check the space dimensions for specific domestic U.S. airlines here.
For trips a week or shorter, I envision what I'll wear each day so I know I'm not taking more than I need. For longer breaks, I simply bring pieces I know I can style in many different ways, such my mint button-down and black skater skirt. In general, I've found it best to err on the side of caution--it feels like a waste to transport clothing I didn't get a chance to wear and working with a limited number of pieces really encourages you to be creative.