About 8 years ago I was searching for a new messenger bag - the one I had was good but too small, its only one big pocket was inconvenient, and the zipper was starting to fail. And since I was planning on bringing this bag with me everywhere, I needed a bag that could survive being dragged on a classroom floor, exposure to sun and rain, and fit under an airplane seat. Anything requiring "gentle care" was immediately out. Backpacks were also ruled out for a simple reason: in my country of origin backpacks are often cut open to steal their contents, so I wanted a bag I could always keep my eyes on.
My first purchase was a Timbuk2 bag which I bought on Amazon because there were no local retailers (looks exactly like this). Their marketing at the time promised "the last bag you'll ever buy" (or something to that effect), which was exactly what I wanted. But you know what the problem with lifetime guarantees is? That you can only judge them with customers who have used them for a lifetime, which disqualifies essentially everything made after at least the 2000s. Luckily (for you) you don't have to wait that long because a year or two after buying my bag the waterproofing started peeling off (along with a bit of the interior). As for the "lifetime guarantee", it turns out it is only valid for customers who bought their bag in an official shop. I got mine from Amazon, so no servicing for me. It has now been relegated to ugly sports bag status.
My second bag is an Aunts & Uncle's leather bag that I bought 7 years ago. The actual model is no longer for sale, but this one is very similar. I chose leather because, unlike more modern materials, I knew this would last forever (we still have bags from the 1800s around after all). And to be fair the bag's exterior is fine - it's a bit beaten up, but that's just part of its charm. The real problem is that the bag doesn't close anymore: the closing system uses Velcro (sorry, "hook and loop") which always made the bag impossibly loud to open. It was loud in daily life, it was loud in a quiet classroom, and it was definitely loud on a train at night. Eventually the material gave up and stopped closing altogether, which made it much quieter (good) at the cost of risking everything falling out (bad). I got in touch with the manufacturer after reading their sustainability compromise to get some proper belts installed, but the only solution they offered was to replace the Velcro and make it loud again.
I'm currently looking into leather working to see whether I could install some belts myself without making a mess. I would love to pay someone to do it, but apparently my city has exactly one woman who could do the job and she's on a sabbatical. I'll also probably peel all of the remaining waterproofing flakes of my other bag, spray it with some generic waterproofing, and make it look at least decent.
What would I recommend to someone who wants "a bag for life"? My suggestion would be to go for something simple that one can fix by themselves: while I currently don't have the leather working skills for doing the job, at least there's a clear path forward for my second bag. But sourcing, cutting and reapplying plastic liner for the first one? Good luck with that.