So it did happened to me not long ago, so I made a very simple ".bat" file that will do the backup of only the modified files (or new files) from a few directories every time I turn off my computer.
...and the good thing are...
-You are going to back up only the data that has been modified. (not need to copy files that you already have in the backup USB pen drive )
-You'll do it when turning off the computer.(you don't mind if it take a bit longer because after it's done, it'll turf off the computer for you)
Step 1: What to backup
Lets say you're interested in backup the information you have in the Outlook, first thing to do is find in your computer were the Outlook stores that data.
In my computer (i'm using XP) is located in
C:\Documents and Settings\("your account name")\Local Settings\Application data\Microsoft\Outlook\
You can make sure that this is the files location if you open the Outlook then Right click on the root folder (probably Outlook Today), Properties, advanced, then look at the Filename box; this is the location of your files.
Although you don't need to back up all the files form that directory, I rather be on the safe side and do the whole directory.
Any other directory you want to backup? all you need to do is find the location on your computer.