Battery life on the 5X has improved over the past week. Perhaps I'm not stressing it as much, or the calibration has collected enough data, or maybe it's the ElementalX kernel and battery tweaks I installed.

Things are definitely better now though.

Here is something I found that has turned out to be nearly indispensable with the new phone and it's USB-C port:

Sony (yuck) 16GB USB A/C Stick

The product photos surprisingly don't show the USB3 Type-A connector that comprises the fat end of the stick, but it's there. Nice and small, not terribly quick at writing, but not that slow either. Reads are very snappy (over 100MByte/sec).