[londons_explore]

hdds act as a big metal faraday cage, and the actual magnetic media will probably survive.

USB sticks the actual flash memory chips have input protection diodes and are quite physically small (limiting the voltage across them), so again I wouldn't be surprised if they survived.

[coretx]

Yes, that's why I wrote that you need to remove the _cover_. Regarding flash memory chips the real worry is to not blast them for too much time, not if the data is purged.