A lot of people backup their files onto a USB thumbdrive or an external hard drive. These devices have high fail rates. They will not last for more than a couple of years. Make sure you backup to multiple devices or a device that has more than one drive in it so if one drive fails your data is still there. We rely on these devices for storing our photos,music, important papers,etc...and often they are not there when we need them. So in short make sure there is a backup of the backup.

Just as important is to make sure you have software that is backing up your important files every day.

An alternative is to use an online backup service. These monthly services are very inexpensive and take care if everything mentioned above.