Day Owl makes backpacks, totes, and cord pouches out of recycled plastic bottles. Since I didn't actually need a backpack when they were doing their initial Kickstarter--and the best way to be sustainable is to not acquire more stuff when you don't need it--I don't have one of their backpacks. But I do have a cord pouch and I quite like it; I've taken it on basically every trip I've taken since I got it.

They've scaled down operations a bit, and are now focusing exclusively on selling their own bags rather than accepting old backpacks for refurbishing and recycling. If you do have an old backpack that needs a proper end, you might try asking Retold Recycling if they'll take it.