I too have been using USB sticks since they first became available and I have a 64M one here that is still working from years ago. The advice to buy quality is reasonable, but in the day job I buy between 30 and 50 a year, usually Kingston and there are still failures after repeated use, even after fairly short periods of time. These seem to be more often down to software on the computers using them as the sticks will usually reformat with the appropriate software, but by then all of the data is lost.
Portable SSDs are basically the same thing, and over the years I have had several hard disk failures.
Saving to the cloud is quite reliable, but unless you have a paid account check to see what your provider guarantees – it is often very little!
The only way to totally guarantee your data is through two things – Firstly redundancy – save your data in two or more places and refreshing – rewrite you data from time to time.
It is up to you to decide how much your data is worth. At home I back up to two different NAS storage systems every so often, and the main one of these is a RAID array.
If this sounds a pain remember that when we used film we all had boxes of negatives and prints or transparencies that, short of a fire, were permanent. Now we use digital photography we are sometimes hard pressed to keep digital files for more than a few years or so. The life of re-writeable CDs and DVDs is 10-15 years as blank disks, CD-R or DVD-R recorded data will be safe for more than 100 years but in the case of the – RW versions it is apparently only 25 years or so.
If that sounds like a long time remember that the first photo of Niépce in 1826 still exists and my own wedding photos if they had been stored on DVD-RW, had such a thing been available then, might not be readable today!