I just spent 4 weeks over seas with just carry on..... I do it because I prefer to travel by train and foot, and often go to out of the way places, where a lot of baggage is a serious burden.

The wardrobe I took was relatively casual, easy to move in, but still nice enough to go out in. It was cold where we went, so I took a lot of wool and cashmere which packs well. I took thick wool tights, skirts and wore a pair of Keens that had a very good walking sole, but a fancy enough upper to look fine dressed nicer. I found a packing method online that allowed me to pack 8 sweaters (4 turtle necks and 4 cardigans) 2 base layers, 4 skirts, 4 pairs of tights, a pair of insulated tights, and all my undergear in one carry-on. My outerwear stayed on me - waterproof/windproof jacket, gloves, scarf hat.
Impressive if it's all in a carry-on. Must enough easy-care, etc. styles. I try to wear something heavier/bulkier getting onto the plane.