Well... to start, you can back up files online or on an external harddrive. You can do so manually or automatically.
What do I do? I don't have much time left.
Quickly, depending on your favoured type of location to store your files, there are different options that all keep your information private unless you want to share with others.
One of the more simple methods are to save your files onto an external hardrive. One of the more popular brands for this year are Seagate, Buffalo, Adata and Western Digital. If you are aware that you sometimes may not remember to save your files, simply get Windows Backup and Restore or Mac 101: Time Machine. They'll save it for you.
I can't really go and buy one in time to save the files. Is there another way?
Of course. Actually, the hard drive did have some issues like the possibility that it may be stolen or destroyed. This brings us to my favoured method: online backups. They are a way that you can actually save your files on the internet or on an application. Simply log into Google or Microsoft and open Google Drive or Onedrive on the internet. That may be if you are able to remember it. If not, get Mozy or Carbonite. However they may cost you.