Shortly after moving here, I bought a couple Western Digital Passport portable hard drives. They were about the size of a deck of cards and plugged into a USB port with no need for a power supply. One drive I kept in a fire and water-proof safe, the other I kept ready to shove into a pocket if I needed to leave in a hurry. The drives were large at the time, 320 and 500 GB, but those sizes have become rather cramped; the 320 GB drive was nearly full. Whenever there was a tornado watch, I'd hook up one of the drives and try to do a backup, but it took so long that the watch was over by the time it was finished.
My new computer has two USB 3.0 ports and Costco recently had the newest model of WD Passport drives on sale, 1 TB with a USB 3.0 interface, so I bought a couple.
The speed difference is amazing. I performed a full backup using both the old and new drives. It took 2-1/2 hours to copy 10 Gigs of data to one of the old drives, but a mere 15 minutes to copy 32 Gigs to one of the new drives! The backup software I use, SyncBackPro, only copies data that has been changed since the last backup, so once the initial data set has been created, it only takes a fraction of that time to do a backup. This means when a tornado watch comes along this year, it should take only a few minutes to do a complete backup of my data. I'll be able to update both my bug-out drive AND the one in my safe.