You can always put the USB stick into a PC/Max and see if it can read it OK. If you do not have a backup you can try taking one at that time and re-writing the USB stick.
i use Sandisk Cruzer fit without problems, but the problem with them can be that because of their small size they are not very good with heat disposal. Something like Kingston Data Traveler (ones with metal case) are a good choice. Note that USB2 versions are recommended as being more reliable (as well as cheaper) than USB3 variants.