Are you looking for a carry bag or backpack?

There are plenty of good 40-50 Lt (2200 to 3000 cubic inch) sized backpacks that could easily carry 40 lbs and not wear out. Just ensure that you spend the money and don't cheap out on the pack. Purchasing a good quality pack will allow dual purpose use and give years of service.

I am sure that 10-15 minutes of research on such sites as REI et al, will prove fruitful.

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Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.

John Lubbock