The North Face Solaris 40
Here's what other sites are saying:
For a gear-intensive day hike up to that high-mountain lake or a quick weekend venture, The North Face Solaris 40 Backpack holds your necessities easily. The North Face's open-air mesh panel down the back of the Solaris 40 Backpack allows airflow between the pack and your back, so you don't end up with an uncomfortable, sweat-soaked shirt as you push through your quick peak-bagging trek.
An exceptional pack for quick overnighters, this 40-liter pack is panel-loading with ample room to stash gear for a day or two. Designed with a large main compartment and lower compartment with a trampoline divider, this pack also contains an easily accessible front stash pocket.