The goliath barbarian pack mule mentioned earlier is likely a combination of things. First you have the default incredibly generous item weight capacity ratios, next goliath doubles that, finally barbarian may be doubling it again on a character likely maxing strength for combat effectiveness giving them a total carry capacity that is probably easily close to if not more than all other characters in the party combined.
I'll admit that I have a lot of trouble getting very excited about encumbrance. For a while in one of my RM games we had an Ogre PC, who could carry a lot of stuff. It didn't hurt the game.I mentioned before that I always lean into container capacity on this one. All well and good that dude can offer a piggy-back ride to a frost giant, but a backpack can only hold 30 lb. worth of gear, so choose your equipment wisely.
As far as containers are concerned, I think the goliath could just pay a tailor/leatheworker to make a bigger one. I'm not a goliath, and I own a backpack that can pretty trivially carry 20 kg worth of stuff (I take it supermarket shopping). It's made of synthetic materials, but I don't think its construction is significantly more robust that what could be done with D&D-ish fabrics.