Great information on backpackers lifestyle and how to pick a backpack that fits your needs: http://www.backpackeurope.com/packing/backpacks.html
I admit to hoarding backpacks. You never know which pack you’ll need for the climate, trip length, culture, road best traveled. Alas, my very first Canadian army surplus pack is gone, but I do have the second, a vintage Camp Trails special with extra cushioning hand sewed on the straps. Saw me through three months of tramping around Italy, including Sicily, Sardinia and Elba.
Then there’s the expensive internal frame model for long-distance trekking that’s been to Kamchatka, the Grand Canyon of Kuwai, the NEK, the DAKS, Algonquin, Central Asia, eastern outposts of Indonesia, Thailand and assorted SE Asian whistle stops between.
The modified mountain pack that saw me across France for 7 weeks of daily walking includes a water reservoir and tube. I used the criss-cross elastic binding lines designed for a mountain axe or crampons to hang wet laundry which swung dry as I hiked.
The latest addition is a slim line model I picked up for a long trip to Tasmania and cities in SE Australia. Until the end of the trip when I started picking up souvenirs and gifts, it held everything.
Speaking of backpacks, this guidebook series might be of interest: