Backpacking. You dont need everything you own or even half of it to travel around the world. Over packing is a common mistake and one way you can put a damper on your travel. I have been guilty of it myself. You can always buy a shirt or something you may need when you get to where you are going. Light is the way to go.
Know the right clothes to take. Clothes should be light weight and quick drying. If you dont wear it at home dont take it on your trip. Chances are you will end up not wearing it and carrying it around. Before your trip, try washing your clothes for your trip and hang them to dry. This way you will know if they will dry overnight or not. If you have to hand wash your clothes in a sink you will not be left with wet clothes in the morning. You can also use bath soap to wash clothes in the sink if needed. Stick to darker colors. They don’t show stains and dirt as badly. I carry three shirts, two pants, three pair underwear. The pack cube organizes smaller items in the pack.
REI Flash 50. A 50 liter pack is the largest you can carry on an airline. Another thing nice about only carrying a backpack is not having to wait on checked luggage, once you are off the plane you are on your way. Also carry a rain cover and a long peice of para cord. I have not had it happen to me yet but if an airline does make you check your backpack. It is posible to put the rain cover on it backwards to cover the straps and then wrap and tie the para cord around it. That will keep the straps from getting damaged.
Know where you are going. There is a ton of information on the web, you just have to find it. Museums, parks, transportation, visas, working holiday. Carry copies of your driver license and passport. In some cases it may be better to give a copy instead of the real thing.
When visiting countries without proper water purification systems, dont drink the local water. It will make you sick. Bottled water or an ultraviolet lamp pen would be a good choice to sterilize clear water.
Talk to your doctor before you go. Know if there are any vaccinations you will need before going. Get a dental exam if going on an extended trip. You don’t want to get to a remote location on a backpacking trip and develop a tooth ache. If you wear glasses, take an extra pair. If you wear contacts, be sure to take enough extra sets to last until your return home.