A couple thoughts.
- You should have the data in more than one location. That means if you don't have it on your laptop drive, you should have 2 (or 3) other locations where it is stored. One of those locations should be off-site, if possible.
- Since this isn't storage that will be not be accessed, it doesn't need to be a standard external HDD, however that option would likely less hassle and possibly cheapest long term.
- SD cards would be a good option. As would
USB ($35 each) drives. Small, easy to store and not going to make you cry if they get dropped.
- Another, kind of outside the box solution, get a
Hard Drive Dock and buy a couple 500GB drives (2.5" or 3.5", it holds both) to store the copies of your data on, then you can get a nice 3TB drive to dock in it permanently. This would allow you to store the drives, have easy access later but still have the dock for use in the mean time. The biggest downside to this is safely storing a naked mechanical HDD is a bit more of a hassle, as you would at minimum want some type of case. (Could even put one together with the static bag and some foam in a small box)
- All those options are going to cost you a good chunk of change up front and be a bit of a hassle. Why not consider online storage? 100GB is $5 a month on Google Drive. Don't need to worry about physically securing the hard drives, if you ever need it, just a simple log in and download, if you want to add more at a future date it is flexible, plus you could use the extra for storing other files 'in the cloud' for other reasons (music etc). Biggest downside would be upload times, especially if you only have a 500kb upload speed from your ISP. If security is a concern, you could encrypt it with something like Truecrypt if you wanted.