Packing clothes that can be worn more than once help a lot. It's not always possible, though. When I am working (meeting clients) I will not wear the same shirt for two days without a wash. Also, on some trips I'm doing two different activities (e.g., meeting clients during the week and hiking in the mountains on the weekend) or visiting different climates so I need 2 separate sets of clothing. That makes it difficult to travel with only hand baggage.