Do you mean that you'll be traveling, perhaps with a MacBook of some sort?
In that case, I'd recommend keeping some kind of external device from which you can boot in an emergency.
It could be:
- an external drive
- a USB flashdrive with a bootable copy of the OS on it
- an SD card (if your MacBook has such a port), again with a bootable copy of the OS on it.
If you're going to be crossing international borders, where there is a chance "the authorities" will take the laptop, boot it, and check your peripherals, I suggest that you do not put anything of a sensitive nature on the drive. Keep on it only what you aren't "afraid to lose".
The idea is to have a SECOND FULLY-BOOTABLE drive at-hand if you need it.