Can I show public holidays?

Yes, on every plan. Open the calendar menu, choose Display Options, and pick a country under Public holidays. Its public holidays get the same shading as your days off, with the date in bold. Hover over a day or open it to see the holiday's name.

Only public holidays are shown, including substitute days. Bank holidays and observances are not. Public holidays are set per calendar, only the calendar owner can change them, and they also appear on the calendar's public page. If you sync Google's holiday calendar for the same country, AnuCal hides its matching events so each holiday appears once.