Backups on two flash drives (thumb drives, etc.--pick your terminology) and on an external hard drive.
I learned to do backups the hard way when sectors on one of those 3 1/2 floppy disks went bad. I worked on the manuscript the night before and saved the files and everything seemed fine. Put the disk in the next morning to work on the manuscript again and for some reason the program told me I had over 1,000 pages in the file. I tried to ctrl+end to get to the end of the manuscript and the hourglass stayed up FOREVER. I finally had to shut down the program because it froze. Tried this two more times with the same result. I finally opened the file and used the page down key and everything seemed to be fine until I got to this one part that seemed to be repeating itself over and over. I closed the file and cried off and on for most of the day. By the time my husband got home, I had the crying mostly under control, but when I tried to tell him what was going on, the floodgates opened again. Thankfully, my husband knows computers and somehow he was able to retrieve the file. He told me to save it to two disks and the hard drive on the computer. The only problem was that it turned out that I had two sections that were repeating themselves over and over, which accounted for the 1,000+ pages in the manuscript. And when my husband recovered the file, those two sections had been removed from the manuscript. That was okay, because they weren't long and I did have a hard copy that contained those two sections.
And once when a computer crashed, I thought I had lost the only copy of a manuscript, but I had emailed it to someone and forgot about it. I was chatting with her and mentioned I had lost the manuscript in the crash, she searched her email and found it. She didn't say anything to me about it, but I opened my email one day and there was the manuscript. She had forwarded the original email to me.
So yeah, I make sure I have more than one backup and I trust them. I've lost a few minor changes in manuscripts since then, due to not updating the backups, but nothing like what I went through those two times.