Here's one for the books: GOP presidential candidate Donald Trump spent nearly $55,000 (£41,600) in campaign funds to purchase copies of his own book. The expenditure, tallied in Trump's most recent filing with the Federal Election Commission, (FEC) was part of a "swag bag" put together for those attending the Republican National Convention, reports the Daily Beast.

The canvas tote bags, stamped with the Trump slogan Make America Great Again, included Kleenex, cups, hats and T-shirts also bearing the campaign slogan and his latest book, Crippled America: How to Make America Great Again.

Delegates were also given plastic foetus figurines. A spokesperson for the Republican nominee told the Beast the books were purchased "as part of gifting at the convention, which we have to do".

The campaign paid full retail price for the books instead of an author's bulk purchase rate directly from the publisher.

The $55,000 (£42,000) to Barnes & Noble could have purchased more than 3,500 hardcover copies or just over 5,000 copies of the renamed paperback release, "Great Again: How to Fix Our Great America."

At issue is whether the Trump campaign funnelled donor money into Trump's pockets while boosting book sales.

The book purchases are part of a pattern of Trump campaign expenditures that heavily favour Trump's own properties. Campaign funds have paid for stays at Trump hotels, events at other Trump properties, and lots of flights on Trump's private jet – all at top dollar.

Trump has nearly quintupled the rent on his campaign headquarters in Trump Tower in Manhattan – from $35,458 (£26,866) a month in March to $169,758 (£128,642) in July – and the tab is being picked up by campaign funds.

Recent filings show that Trump's campaign paid his golf courses and restaurants more than $260,000 (£196,999) since it agreed to a joint fundraising deal with the Republican National Committee in mid-May.

Earlier election filings showed that 17% of campaign spending – some $11m (£7.4m) – had been paid to Trump operations from the start of the campaign to June.

Trump boasted in 2000 that if he ever ran for president it would be a money making, not a money-losing, operation for him.

"He could end up turning a profit if he repaid himself for the campaign loans," Paul Ryan, FEC program director and a campaign finance expert with the Campaign Legal Center, has told the New York Times. "He could get all his money back plus the profit margin for what his campaign has paid himself for goods and services."

The circular books sales could end up being a problem. It could be illegal if Trump receives royalties from them.

It would be "impermissible to receive royalties from the publisher" in this case, Ryan told the Beast. "That amounts to an illegal conversion of campaign funds to personal use. There's a well-established precedent from the FEC that funds from the campaign account can't end up in your own pocket."

Federal campaign law dictates that campaign spending must not "result in the conversion of campaign funds to the personal use of the candidate or any other person."

Donating those royalties to charity "might be a permissible arrangement," said Ryan. "But the bottom line is, no money of this $55,000 from the book can end up in Donald Trump's pocket without violating federal law."