1. Ravpower file hub to an external Hdd as big as you want.
2. SanDisk iDisk. Lightning / usb flash drive.
There’s ways.
hum...
Let us see:
You bring your iPad outside for the portability. Then you went to carry an file hub and external hdd. Work as intended.
2. I got by 128GB SanDisk USB drive for 30 bucks at Costco. Same storage option, lightning based USB cost more than 120 dollars.
In the conclusion: There is no easy way or cheap way to transfer file between external devices and iPad without using iTunes or third party software/hardware. Where i can just plug in USB devices to my laptop or Windows tablet and transfer files between without much issue.
Maybe there are rich Apple users that just can buy all the dongles and adopters, but I am not willing to shell out tons of money for things just work with iOS devices.