My daypack (9 yr old Northface Recon) has a mesh back. One day I decided to try fitting my hardhat in it -- that was a mistake because now everything is stretched out. I don't use it a lot because there is no way to secure the top and smaller items can fall out. I do find it handy for wet items to hang out for a while - like a rain jacket or hat. I found I used it for things like gloves and my maps for ready access. It also comes in handy while geocaching because I can carry a ziploc bag of goodies for trading and refurbishing older caches.

It also has 2 mesh pockets on the sides that are great because they can be used for either waterbottles or in my case my camera and GPS. They can be cinched down tight with cord locks, nothing has ever fallen out. They don't seem to a problem snagging on anything in the bush but then again I try to stay out of the real dense stuff! The back pocket is the one that snags for some reason, maybe its because of my ducking under branches but I always seem to have lots of tiny twigs collecting in it.