If your able try to get either a usb thumb drive or external hard drive and every now and then backup the really important things only to it. Then have that drive unplugged.
2 reason for this.
1. In a bad enough storm, if a lighting strike hits the power lines close it will fry everything in the system, including both drives (This is rare but I have seen it happen. One friend sent me a picture of a hole burned through his motherboard from a lighting strike, the whole was the size of a golf ball).
2. Viruses, unknowing users or just bad luck. With both drives being in the system any one of these things could delete the files.
So by having a backup that is not hooked to the system you keep it that much safer. Myself, I have 2 external drives. 1 stays in a small water proof and fire proof safe while the other is backing up. Worse case situation my work is safe
Shane