1. Boot your USB

2. Open terminal (ctrl+alt+t)

3. generate a key (eosio-keygen)

$ eosio-keygen

4. Save the key in a)  a file or b) encrypt it in keepassxc

    a)  eosio-keygen >> Desktop/filename

$ eosio-keygen >> Desktop/filename

    b1)  windows + r (search for keepassxc)

    b2) Open and create a database, with a secure password. This password is later used to access the keys, so make sure you know it.

    b3)  Add new entry (ctrl+n), enter private key in password & repeat, enter public key in Notes, Apply.

5. Move the file containing your keys onto a second USB, that you use to store your data.

For detailed walkthrough:

a) Generate key to file b) Generate key and encrypt it