Bring only carry-on luggage, if at all possible. That means only bringing little bottles of shampoo, toothpaste, etc. and buying larger bottles when you travel. As for the multi-purpose knife, buy it when you get to your destination.
The first two backpacking trips I took (6 weeks in Europe and 6 weeks in China) I brought full hiking packs. I then realised that I hated the added stress of (1) airplanes losing my bags (2) waiting for my luggage at luggage pickup (3) being separated from my luggage on buses (4) having to shove my luggage into teeny lockers at the hostel, etc. I have since traveled only with a carry on and my travels have been simpler and less stressful.
Rick Steves has a pretty good packing list here. I use the eBag weekender convertable carryon tls and it serves my needs perfectly.
