Satoshi,

I'm not sure that you need a heavy pack. I sleep in a camping hammock--my pack, food for 3 days, sleeping gear and other equipment comes in well under 15 kilos for summer in the mountains.......less than thirty pounds--that's with "luxuries" like camera and fishing equipment. If I want to, I can trim it down more--I can easily get under 10 kilos but I like a bit of comfort luxury such as the hammock--pure sleeping bliss.

BW