In addition to backing up your data you should be prepared to reinstall your software.  For most software the two items that you will need are the installation files and the license key.

• If you received disks when you purchased your software, be sure to keep them in a safe place.  Notice where the license key is located and be sure not to toss it out with the packaging.  It should be kept with the disks.
• If you downloaded your software, you probably got a e-mail with the license key.  Print it out and save it with your software disks.  You will probably be able to download the software again but if your computer has a CD or DVD burner you might want to burn a copy to a disk and keep that too.