+1 for Deuter EXP Air range. Bought the 15ltr Race exp air for running/walking about 12 years ago. After near daily use, the zips started to give way last year. And that was my fault. Tried to cram too much in too many times. Bought the slightly larger 20ltr version. It's less suited for running, but is a great all rounder (and better for me for cycling than the previous one). Hiking...Absolutely awesome. Plenty of room, Pole strap attachments, place for a rear light (great for cycling, good for night trekking when in groups), in built rain cover.
With both of the above, I used the gap between the mesh and that rucksack to hold a foldable/rollable item that wouldn't restrict the airflow. (map, sit mat, sun hat, that type of thing) that might sometimes need quick access. They have never fallen out either.
