Sadly, data theft is an incresingly common crime these days and there are plenty of digital bandits who would be only to willing to pilfer your files for juicy information.
Aside from learning the finer points of cryptography yourself, you could install Paragon Encrypted Disk to create 'images' in which data is encoded.
These images can be either 'mounted' or 'unmounted'. When a disk is mounted, it means it is active and you can use it like any other local disk, copying files and folders, and creating and editing new files.
The difference is that the disk is totally encrypted with powerful algorithms, which are completly transparent, leaving you free to get on with your work without having to worry about the data being unsecured.
When you unmount a disk it means its contents are completly unaccessible anymore. You can then write this container file to any compact media such as a CD, DVD or USB stick and always carry the encrypted disk with you without fear of someone getting hold of your data if you lose it.