When you go out into the outdoors you need to carry a certain amount of gear with you. This is too keep you warm, dry and safe. You need a backpack to carry this gear in, it needs to be strong, comfortable and fit for the task you set it.
I use a variety of packs depending on the type of trip: small sub 35 liter for day walks, a 55 liter bag for overnight and a larger 65 liter version for multi day trips.
My Vaude Astra 65+10 mulit-day pack
My current multi-day pack is a Vaude Astra 65ltr + 10. It is slim, almost like a mountaineers style pack but still large enough to carry 3-7 days worth of gear in. This pack is made by Vaude, a well regarded German company who produce a range of excellent outdoor goods.
Its a touch (just a touch?) heavy at 1.9 kg, but the harness setup is excellent, so far I have had no trouble with it at all.
Harness setup on the Vaude Astra
I have an ongoing project to get my base gear weight down to 10-12 kg without water and food, I'm currently around 14 kgs (2016 Update: now at 10.5 kgs!). When I get my base weight down I may look at buying a lighter pack for shorter overnight trips.
The Astra on the Casey Binser Loop, 2012
Wearing the Vaude pack on the Wharfedale Track 2014
I brought this pack from Complete Outdoors, a Christchurch outdoor retailer. The pack cost me $275 NZ dollars, a fair price for a pack of this size/type.
UPDATE: Feb 2016
The Astra on the Queen Charlotte Track, 2016
I've been using this pack for nearly 6 years now and it has proven to be one of the best pieces of kit I have invested in. It is very comfortable even with a moderate-heavy load and over distance. It has worn well, hardly any wear at all really,
I am really attached to it as we have shared many an adventure over the years. I expect it will be with me for years to come.