Generating a passphrase using the diceware method, all you need is a die or five.
See HACKING on how to build diceware.
Here is how it looks when generating a weak three word passphrase using the EFF wordlist, the Diceware list and the alternative Baele list.
$ ./pre-inst-env scripts/diceware ~/Downloads/eff_large_wordlist.txt ~/Downloads/diceware.wordlist.asc ~/Downloads/beale.wordlist.asc
Welcome to diceware (press Ctrl+d to exit)
-- Please roll five dice and type in the number: 31434
[ eff_large_wordlist.txt ] Current passphrase: freebee
[ diceware.wordlist.asc ] Current passphrase: goode
[ beale.wordlist.asc ] Current passphrase: grady
-- Next number: 14236
[ eff_large_wordlist.txt ] Current passphrase: freebee brought
[ diceware.wordlist.asc ] Current passphrase: goode bird
[ beale.wordlist.asc ] Current passphrase: grady bits
-- Next number: 13426
[ eff_large_wordlist.txt ] Current passphrase: freebee brought bleep
[ diceware.wordlist.asc ] Current passphrase: goode bird batik
[ beale.wordlist.asc ] Current passphrase: grady bits bay
-- Next number:
Your passphrase using eff_large_wordlist.txt is "freebee brought bleep"
Your passphrase using diceware.wordlist.asc is "goode bird batik"
Your passphrase using beale.wordlist.asc is "grady bits bay"