Many modern portable hard drives already come with hardware encryption, but if you have extra 2.5″ hard drives, you can turn those into secure storage devices with the LockDown USB 3.0 enclosure from Satechi.
The LockDown has a touchscreen keypad and LCD screen to facilitate password entry. It uses AES 256-bit hardware encryption, and you can use it with any OS or USB-based device. Here’s Satechi’s setup video for the LockDown:
Turn on private browsing and head to Satechi’s website to order the LockDown. It sells for $99 (USD), which isn’t too bad considering it comes with a USB 3.0 cable, USB-to-DC cable and screwdriver for assembly. Note that the encryption will still protect the hard drive even if you take it out of LockDown, so you can make and swap out multiple encrypted hard drives. Just make sure you don’t lose the enclosure, or you’ll never access your data again.