There are an infinity of "what to bring" lists for this kind of journey over the internet. So, i'll just use my own, the one i've always used, even for trips lasting only a few weeks. After all, clothes can be washed, and the rest remains pretty muchthe same stuff, unless it breaks.
"Your bag is your life","Your bag is your home", and so on... these sentences are found all over the place, some are true, others just exaggerations. Of course, when staying away a couple of years it will eventually become like a part of your body, like a shell for a snail.

As for the weight, everyone agrees: The lighter, the better. But it depends on you, if you have no problems carrying weight, load on! But if you're just a normal guy as me, pack as light as possible =)


Enough talk now, here is my list (Including what you're wearing at the departure!):


Clothing


Instead of trunks, girls can take their swimming suits, as long as you keep in mind that in some parts of the world, women bathe fully clothed, either because of tradition or religion.
Instead of the shorts or convertibles, you can take skirts, just not too short, always because of the modesty issues around some countries


Essentials



Keep in mind, this is the stuff i take, and i use a 60L internal frame backpack. Your needs will be probably be different. This is just to give you an idea.
Another thing, it should all weight below 12 kg. Or if you are confortable carrying lots of weight, make sure it doesnt surpass a third of your whole body's weight.