I bought a multi-port flash drive for my brother who wanted to swap files between Mac and iPad without using Bluetooth or Wi-Fi. This is the one which seems to work OK after understanding the instructions about using the downloaded Y-disk App from the Apple Store: Y-Disk Multiport 256GB Flash Drive
(Sorry for the late response I was on holiday when you posted)
If you buy one and find the interface unfathomable then contact me and I'll let you have a set of simple instructions I made for my brother (who prefers to rant and rave at computers rather than patiently learn how to operate them).