so what's the best option? burn a cd?
NO! CDs are even worse, as they will degrade over time. Flash drives wear with use, so dropping some files on them and sitting in a safe for 50 years won't hurt them.
You drop a burned CD or DVD in a safe for 25 years and they'll be junk.
Agreed. No CD lasts more than a few years, that's even if you never scratch the thing.
I can only repeat I've used USB drives for 5-8 years now, without a problem. More reliable than hard disks, CDs