Like bamboola, I fly with carry-on only no matter what length of trip. (1) Plan out very carefully exactly what you are doing on which days, bring clothes that can be mixed and matched to suit various occasions, and plan to re-wear every single item of clothing at least twice. (2) Do laundry during the trip, whether in the sink, using the hotel laundry, or at a laundromat if you will be able to go to one. (3) Get less obsessive about your toiletries. Hotels give you shampoo, soap, moisturizer, and (often) conditioner. Use travel sizes. Buy things at your destination, if necessary.