>>2496297Lurk on ebay. Don't get a shitty old ""vintage"" 70s frame pack (ebay is flooded with them, as you'll find out), rather keep an eye out for more recent production with advanced construction. I got a fantastic Haglofs Skarja X from like 2005, pic rel (seems to be a slightly older model, mine has more modernized mesh carrying straps, otherwise identical).
Alternatively you can look into milsurp, but that stuff will be really hit and miss. I have a nice canvas ludvig ryggsekk which is good for lighter loads (work, groceries, picking up mail etc) but I probably wouldn't want to carry an entire backpacking setup in there for 8+ hours a day. The issue is that it doesn't have a hip belt for weight distribution, so it all rests on the shoulders.