The natural side effect of packing light is that if you are gone for more than a week then you need to do laundry. Here are my thoughts and experience on the options available:
Traditional Washer and Dryer: This is the most expensive option in terms of both money and time. If your hotel/hostel doesn’t have facilities then you need to find a laundry matt. You are also committed to staying still to watch your items (and switch from washer to dryer) for 1-2 hours. However, this is the most satisfying as you know your clothes are clean and you don’t have to continuously try to get everything dry.
Liquid soap: This is the most intuitive for hand washing. However, if traveling light and trying to get by with only a carry on, this will count against your liquids and has the potential to leak. But this option is nice if you have sensitive skin like I do and want to use a less abrasive detergent that you bring from home.
Single Soap Bar: This is a favorite option for those hiking the Camino de Compestella. They have one bar of soap they use for their hair, body and clothes. This is obviously the lightest and most efficient option and I admire them for it. Dr Bronner’s bar of soap was the most popular that many Pilgrims swear by.
Laundry Sheets: They resemble a dryer sheet but are for laundry. They are light weight and compact. I love them because they are suitable for both a washing machine or you can wet them as use them as laundry soap.
As with all my advice, I say it depends. When traveling in winter for two weeks through Eastern Europe or South America, I opted for a traditional washer and dryer half way through my trip. However, when walking 18 days through Northern Spain on the Camino de Compestalla I wanted a light weight option to do laundry more frequently (about every other day). For this trip, my laundry sheets were perfect — they gave me options to wash clothes in the sink (or shower) but also to use a washing machine when available.