>>255134I know your point is to recycle stuff, but...
From my experience, PET is not the easiest material to get a permanent and strong bond by gluing. Certainly not with hot glue!
Just keep that in mind when using that. I wouldn't want a bunch of plack pepper/cayenne pepper/salt/fishing hooks/whatever dumped out into my backpack.
You can buy the things plastic bottles are made out of (see picture) pretty cheap. I would highly recommend those instead.