Here is an article from Lonely Planet on what to pack in that backpack of yours,click here for the link or below is a sample of their article.
Where are you going? Round the world (RTW)
How to fit kit for two hemispheres into one bag? Doing so is the key to packing successfully for a true RTW trip. Consider what you can ditch as much as what’s essential. If you need heavy trekking boots and a down jacket in New Zealand or South America at the start, but won’t use them again as you travel via the South Pacific/Asia, consider sending stuff home as it becomes redundant.