You can get some rather large USB sticks these days. Amazon is awash with 928Gb units for about £10 which are probably not the best. A 256GB or 512GB from a known brand is around £30-50. There are several USB ports on a Pi and you can always boot off a SD card.
Finally, if a network is available then network boot and use NFS or whatever.
The RTC is a cool addition and long overdue. At work I have three Pi 3s with GPS hats and aerials acting as stratum 1 ntp servers. The hats have a RTC included which is handy after a reboot. My use case is "reasonably accurate and stable time" so sub milli second is good enough, I'm not too fussed about nano seconds! I want logs to correlate and desktop clocks to be reliable.
Finally, if a network is available then network boot and use NFS or whatever.
The RTC is a cool addition and long overdue. At work I have three Pi 3s with GPS hats and aerials acting as stratum 1 ntp servers. The hats have a RTC included which is handy after a reboot. My use case is "reasonably accurate and stable time" so sub milli second is good enough, I'm not too fussed about nano seconds! I want logs to correlate and desktop clocks to be reliable.