I have a 512GB microSD card in my current phone that is about half full. I don't have any interest in paying a subscription to store my stuff on someone else's server ("the cloud"), when the SD card only cost me a couple of months of what a subscription would. I periodically back up the SD card at home.

As to what's on it? The usual stuff like pictures and videos, but also game ROMs, call recordings, shows/movies, ISOs, utilities (I can make my phone appear to be a flash drive, bootable even). I also backup my texts and other records using a third party app. When I do have to swap phones, transferring the SD card over and then restoring stuff like settings, messages, records, etc is way faster than any of the OEM transfer tools.