I had the opportunity to do a few day walks while on holiday in Tenerife, so I was looking for a hydration pack that would also swallow all my day gear as well. The Camelbak Volt 13 LR was my choice, and although its designed as a bike pack the bike specific features are fairly nominal - like the hooks for attaching a helmet - ideal for attaching other things.
In use I loved the pack - the hip belt pockets are really spacious and swallow a suprising amount of gear. The main compartment, outer stuff pocket and outer zipped pocket all work well together - even when quite full they don't interfere with each other. When one pocket is stuffed to capacity it will limit what you can put in another.
The profiled foam back contained within mesh produces about the best venting you will get on a pack of this weight and size.
I found the 3L bladder easy to fill, and with access from the back panel I didn't need to empty the pack to get to it - also the bladder holds the water round your hips close to your centre of gravity - great for stability and ease of carrying.
I liked this so much that I'm going to continue using it as my summer daypack - even though I rarely need 3L of water (and I don't have to fill it anyway). I was pleasantly surprised how much gear I could get into the 13L cargo load and really please at how all the pockets worked to keep me organised.