Flash Drives: Probably the most common back-up media are USB flash-drives or thumb-drives. These are small, convenient, reliable and very inexpensive. Copy all of your files to a thumb-drive and your backed up. Sizes range from 2 GB to 256 GB. Prices begin at about $5 and up.
External Hard Drives: If you need more storage space you may opt for an external USB hard drive. You can get these any size up to 3 terabytes. Price start at about $35. I really don’t care for the 3.5″ portable externals. I think they are fragile. If you need one for the portability then go for it but don’t buy one because they are cheap.