At the title screen, copy and paste them in the bonus code button,
after you activate the items in your avatar so you can put on your
Best-VA – Unlock April Fools „High-Quality” Voice Acting, you can
also disable voice by re inputting the code again.
Holiday-Man – Unlock Holiday Man Christmas quest.
WoN-Boots – Unlock sparkly boots.
(decent stats, mostly fun for the on-screen effects)