I’m not terribly skilled but I can sew a bit and have a White Jeans Machine I bought specifically for doing my own repairs and making canvas utility bags. Problem is I haven’t been able to find high quality thread that matches the weight of denim or light canvas. I use mostly Gutermann thread which is excellent quality but lighter weight than what I want. Best I have found is “denim thread” in Wally World but the quality is not so great and it’s only available in gold and blue.
Look for quilting thread, which comes is a wide variety of colors.
Dollmaking thread is very strong - I use it for sewing things that will have a lot of abuse at the seams.
Downside is it’s difficult to find in any colors other than white, beiges and browns. But it does exist.
Or read this page for the weight of thread that you’ll need. I repaired a garmet bag with Heavy Duty thread and so far, it’s held up great. This place made me a happy camper when I needed to purchase thread for my Serger. You might want to check it out.
There’s an outdoor fabrics store around here that sells Kevlar thread. Only in black, though…
You could probably get good hints by talking to a cobbler or outdoor gear/ luggage repair place…
There’s a lot of heavy thread out there, but not much of it can be used in a regular sewing machine. Coats and Clark makes an all-nylon thread which works very well, though. I think it’s called upholstery thread.
I’d be tempted to use beading thread, which is plenty heavy-duty and if it’ll go through a beading needle, you can thread it through a sewing machine.
If you’re making a packsack, or something that will take mucho abuse, I’d recommend reinforcing stress points by hand with waxed nylon - that imitation sinew stuff. YMMV - I’ve only worked in moosehide and know a couple people that made dog harnesses and packs out of canvas.
Padeye, you should be able to pick up some “cable lacing” from the pre-x or whatever the nav calls it these days. You are still in, right? If not, most electronics supply warehouses will carry it. Failing that, check out some sailmakers - not many in Phoenix, perhaps, but prolly lots on the 'net. As an aside, are you still into black powder firearms, or have you graduated into the smokeless powder era of today? I need some info on your area of the country.