Big ass bag? I've got one of these and love it. (I know you were talking about a different style of bag) This is the XL, they make an XXL. I can't emphasize enough how durable and heavy duty everything about it is. All of the various straps and webbing allow you to compact it down to a smaller size, or anchor it on a roof top. This type of bag can be a big advantage when flying (with friendly airlines like SW) because it can allow you to re-shape to fit within the size limits (but don't put valuables in checked luggage, and make sure all your straps are secured so they don't hang up in conveyer belts). The material is a heavy polysester with a plastic coating. So you can put non-waterproof bags in it, and get quite a bit of protection.
It has straps that allow you to wear it as a backpack. Desperate times call for desperate measures!
http://www.rei.com/product/804288/the-north-face-base-camp-duffel-x-largeI find the type of event, and distance, make a big difference in what I bring. And some things really don't belong in the same bag. A strategy of using multiple smaller bags and putting them in a larger bag can be good. They also allow me to plan a little better. I can have a small "actives rig bag" that goes into a larger bag that holds larger pre-amps. Same for photo gear - I think it deserves a separate bag from recording gear.
Where I get into trouble are situations like "last night I recorded with the ceiling rig, today I am going into the woods to record nature and shoot photos". That leads me to reconfiguring my bag, and that can cause you to forget stuff. And you don't want to take an oversize bag that is half empty.
For serious weight or distance, or hiking, I think backpack style straps are essential to distribute the load. The thing about your back is, if you say "I'll just tough it out!"... That toughness can result in a permanent injury - it's not like your quads burning as you bike or hike. And a lot of those back and shoulder injuries tend to build on themselves and not heal.
In terms of carts, you can buy cheap carts that fold up small, and they are great for some gigs. I would avoid bags with built-in carts. Sometimes you want to bring all your gear into a venue in one trip, for security reasons or whatever. Carts are great.
Also, I like to clip my bag to a rail and get it off the floor whenever possible. That is usually via webbing and a carabiner. And when doing photography, I often hang my bag from the tripod to dampen vibrations and increase stability. It also keeps my gear bag out of the mud and sand. That doesn't always work so well with mic stands.