My North Face Recon backpack has two mesh side water bottle pockets. Each pocket has elastic cord with a slide lock. You just put in the bottle, slide the lock tight then loop the loop on the other side of the lock over the neck of the bottle. Since it is elastic, it stays tight. I have never had anything fall out.

The pockets do snag occasionally, but so do straps, etc.

The Recon also has a large outside mesh pocket on the back. This also has a fastening clip. I have it stuffed with small things (mostly snacks) and nothing has ever fallen out. The mesh makes it much easier to find things.

OK, I hate to admit it, but it was my SO's idea to use the excess end of the loop to put over the bottle neck.