I think polyester or nylon reinforced vinyl is a good material for bags and stuff- either the heavy duty truck-tarp stuff alone, or get the lighter stuff to use as a liner with a cordura outer.
What’s your case for not just using carhartts?  Or buying the single layer carhartts and sewing on a cordura front?  That sounds more comfortable to me, and making pants with heavy material is a royal pain- I did once make myself a pair of waxed canvas pants, a la filson double tin pants, and it’s time consuming to manage the fabric into the right place while you try to fell those leg seams.  Carhartts work well, and they’re cheap if you stock up at Sierra trading post when you have a coupon.  I built trails in washington, and also helped out with the horse and mule packing we did.  I thought canvas held up well, and it was pretty easy to wash, either in the machine or with a hose and a stiff brush.  For raingear, I would usually wear a light goretex shell underneath a waxed canvas jacket- the modern shell doing a much better job with having a comfortable hood  and keeping water from running down my sleeves when I was working with my hands up.
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