If you have a spare USB drive, or pick one up cheap, you can easily back up your Mac using Time Machine, so if the worst should happen, you don't lose anything.
Just format the drive into MacOS Extended using Disk Utility (Apps>Utilities Folder>Disk Utility) then plug it in. The system will prompt you as whether you want to use it for Time Machine, choose yes. From here you can choose which folders you want to ignore in the backup, and which you want to include.
Let the machine do its thing. It will take longer the first time as it has to back up the entire drive, but after that it will only back up the changes you have made.