When I was a kid, my dad owned a pickup truck in Mississippi, and there seem to be tons of ways of avoiding getting the groceries wet, a bed-width toolbox behind the cab was the simplest way (and this was way before extended cabs were a thing).
If you are living in such an area where they can't even figure that kind of thing out, it sounds like there might be something in the water.
When I was a kid, a normal-sized American adult could open up a bed-width toolbox, look down inside of it, and easily remove a few bags of groceries before re-closing the lid -- all while standing flat-footed on the ground beside their normal-sized American truck.
Things are not that way anymore; trucks got bigger.
The top of the bed rail of an F150 Lightning is around chin height for a lot of folks: https://imgur.com/ZBOBqJc
Oh, I was a smaller kid back then and I guess I wouldn’t find it very accessible either way. Also my dad was tall. Coolers fit in the back also if you want to use those instead.
If you are living in such an area where they can't even figure that kind of thing out, it sounds like there might be something in the water.