I don't get a lot of chances to do real backcountry hiking, but on this last trip I went up and down (and up and down) the mountains of Peru carrying a daypack. Mules had most of the heavy load, but I used this Lowe Alpine Centro 35 daypack to carry all the essentials along the way. Water bottles in the side pocket, camera and changes of clothes in the middle, all the little items in the top zippered pocket.
I've had my eye on this pack since my last Peru trip. Then I hiked the Inca Trail, my back constantly soaked from the pack resting against it. Meanwhile, my guide was cool and dry because his Lowe Alpine pack had a mesh backing keeping the pack suspended away from his clothes. It was my turn to stay comfortable this time. The mesh backing on this daypack does let the air flow through nicely and it's quite comfortable in varied temperatures.
Otherwise, it's what you would expect in a daypack and more. The overall design follows what seems to have become a standard now: internal support frame, deep interior compartment with cinch strap closing, front compartment for flat items, two mesh side pockets, a foldover top flap with roomy zippered pocket, another small zippered pocket on the front, and a side zipper to get in without opening up the whole contraption. Traveling around the world with this setup would drive me batty, but for moving through the woods and only getting into it now and then, it's ideal. Plus it comes with a built-in rain cover (the orange part here) that tucks away in a bottom flap when not needed.
There are padded hip straps and a sternum strap that can be adjusted horizontally and vertically. At 3 pounds 3 ounces, this is not the lightest pack around, but it is extremely rugged and can be jammed to capacity without worries about splitting a seam. It holds 35 liters (2,100 cubic inches) and has all kinds of loops and straps for adding things to the outside of it. A very good mid-size backpack for your next hiking trip, from a company with a solid reputation: Lowe Alpine. Highly recommended.
I can't get a direct product link to work on the Lowe Alpine site, but see the whole line of Lowe Alpine products and click on "hiking" for the various daypack options.
As a commenter pointed out, there's a "35 + 10" version of this that lists for $179 instead of $149.
Lowe Alpine Airzone Centro 35 at Amazon
Get the AirZone Centro 35 Pack at Backcountry.com