Packing Hints

As we get ever closer to our departure date, we are starting to consider packing the suitcases. When you consider that we have all weathers to cope with, we have something of a problem. We only have 20kg each for allowance. We have 40+ degrees and dry as a bone in Ayres Rock, 99% humidity in the rain forest around Cairns the next day, and below zero on Fox Glacier in NZ 10 days later. All countries in the southern hemisphere will be in their summer and LA, San Francisco and New York will be in their Winter.  So far we are packing some clothes that we are prepared to throw away once their job is done. Some of our India hotels are rather posh and jeans and tee shirts would not be acceptable there. So what do we pack?  If there are any seasoned globetrotters out there with hints and tips for us we would be very pleased to hear from you.