Trump has probably spent more on hats than he has spent on direct mail. The campaign filings occasionally aggregate a few things from the same vendor under one line-item, so some of the hat spending was on collateral generally that includes some hats. (His campaign spent more than $2 million on a line-item that was exclusively hats, though.) Overall, Trump's spent about $15.3 million on collateral — shirts, hats, signs, etc. — more than he has spent on field consulting and voter lists and data.
He has spent at least twice as much on collateral as he has on payroll.
In one apparent concession to the traditions of running a political campaign, Trump has at least started spending more on ads. The FEC reports don't go into great detail about what is or isn't ad spending, so for our purposes we included things like direct mail, telemarketing services (which probably went to fundraising), the campaign's website and digital outreach and so on. You're welcome and encouraged to take issue with this categorization, but it seemed appropriate.
That said, Trump spent more on ads (in that broad sense) in September than he had in any previous month, and also spent more as a percentage of his overall spending. It's not a surprise that the majority of his recent spending was on ads; what's surprising is that in 11 of the 16 months he's been running, ad spending was not the majority of what he was spending on.
Nothing encapsulates Trump's primary and general election campaigns more neatly than his spending on collateral generally, and hats specifically. Most candidates dream of seeing people clamoring for shirts and signs bearing their name or campaign message, but only a select few actually engender that kind of interest. Donald Trump did, and the force of celebrity that made his hats hot items also powered him to a plurality of the vote against a wide field of Republican opponents.
In the general election, that wasn't enough. His spending on polling was reported only in the last two months, a period that overlapped with his hiring Kellyanne Conway, a pollster, as his campaign manager. She has tried to get Trump's campaign to look more like a traditional one, with mixed success.
But Trump has still spent more on hats than polls and more on collateral than get-out-the-vote tools. The campaign in a nutshell.