Western Digital My Passport or something similar. Cheap and I have a couple in a drawer for backup and safe keeping. My oldest one is about 12 years old. I plugged one in the other day and still works fine and everything is there.
When I master projects, in addition to the release medium , I produce 2x archival Blue Ray and 2x thumb drive, labeled, with read-me files explaining as much as possible what's there. I put one of each in storage in different locations.