Next month's 'Reason Rally' in Washington is expected to attract around 20,000 atheists, including actor Johnny Depp and other big-name speakers like Bill Nye and Lawrence Krauss.

As well as fiery speeches against religion, however, participants in the June 4 event will be given a voucher for a Subway sandwich and a free book – both courtesy of a New Zealand-born evangelist.

Ray Comfort, who hosts popular TV show The Way of the Master, is donating $25,000 of gift vouchers and a book entitled Fat Chance: Why Pigs Will Fly Before America Has An Atheist President.

Comfort said: "Most atheists don't know that there's never been an atheist president, that no member of Congress is an atheist, that in some states it's illegal for atheists to run for office, and that recent surveys show that atheists in America are about as popular as rapists. It's a fascinating read."

Comfort is appealing for volunteers to help his outreach at the event through his Living Waters ministry. While the Reason Rally takes place at the Lincoln Memorial, Comfort and his followers will be filming open-air preaching at the other end of the Washington Mall for his TV show, where he said "we're sure that we will get a few colourful hecklers".

As well as the books and Subway vouchers, Comfort's team has prepared specially-printed currency showing Donald Trump and Hillary Clinton. According to Christian Newswire, Comfort said: "The $25,000 worth of gift cards are a little something for them to chew on (we are hoping to feed 5,000 – it's been done before). This is a small token of our love for atheists, and when we run out of books and gift cards we will give them millions of dollars."