Memory sticks

painted

I wanted several to put our music on to, each memory stick having a different genre, so they would have to be portable and be able to be put onto a keyring or similar

If I were to get an external HDD (for other stuff) which would you recommend?

Nilrem

For external drives it depends on what you're using it for and how much storage you want.

For example if it's something to carry from time to time a 2.5" drive that is powered from the USB is good if you only need a TB or so.

I use Seagate Desktop Expansion drives for my USB drives, as you can pick up a USB3 version with 5TB of storage for about £110-120 (they vary a lot in price on amazon, at the low end they're £110, often £120, but can go up to £160+).
For me they're ideal as they just sit on the desk behind the monitor and are actually cheaper than internal drives.