At an event dubbed the "big reveal", several leaders are due to announce new deals with defence companies, plenty of them in the United States.
Trump has branded NATO a "paper tiger" that would cease to function without American arms and leadership.
"We will announce tens of billions in new contracts that will provide the crucial kit we need to deter and defend," NATO Secretary-General Mark Rutte told reporters on the eve of the military alliance's two-day summit in Turkey.
The defence industry splash comes a few weeks after Rutte tried to ease US concerns about NATO spending with a new pitch using a chart labelled the "The Trump Trillion" - showing $US1.2 trillion ($A1.7 trillion) in spending by European allies and Canada since 2017.
Far from being impressed, Trump said he was still disappointed at some NATO allies' refusal to join the Iran war, which he had launched alongside Israel without consulting them.
"We don't need their money - we don't need anything," Trump said.
"I just want loyalty."
Among the contracts to be unveiled, many of them drawn up and some signed long before the summit, is expected to be one to replace NATO's ageing fleet of surveillance planes.
The summit is being held in President Recep Tayyip Erdogan's sprawling palace compound in Ankara and Trump has suggested he would come bearing gifts for the Turkish leader.
But speaking Monday on the Fox News, Israeli Prime Minister Benjamin Netanyahu urged the US not to sell F-35 fighter jets to Turkey, saying Erdogan "calls openly for the annihilation of Israel".
Turkey and Israel have acrimonious relations.
Erdogan frequently accuses Israel of committing genocide in its war in Gaza, triggered by the deadly October 7, 2023 Hamas-led attack on southern Israel.
Turkey was barred from the F-35 program in 2019 after it purchased Russian-made S-400 missile defence systems.
However, Trump, who has warm relations with Erdogan, has hinted that the sales could soon resume.
The focus of the summit is a stronger Europe for a stronger NATO after the Trump administration warned the allies they must handle Europe's security alone as the United States focuses on China and the Indo-Pacific region.
The Pentagon wants a reboot and is promoting what it calls "NATO 3.0", a vision of the alliance in which Europe assumes greater responsibility for its own defence, freeing the US to concentrate on other priorities.
But hiking defence spending means increasing taxes or diverting resources from other priorities.
UK Defence Secretary John Healey unexpectedly quit in June, saying the government was not willing to spend at a time of rising threats.
Concern is mounting among some northern and central eastern countries that Russia might be preparing a hybrid attack - a combination of conventional warfare with tactics such as cyberattacks - on the continent as Russian President Vladimir Putin struggles to secure victory in Ukraine.
Keir Starmer's office said the British leader would be "focused on building a stronger and more European NATO" on what is likely to be his last foreign trip as prime minister.
Starmer, who announced his resignation June 22, has faced criticism for the slow rate of increase in UK military spending.
His government has committed to reach the NATO budget target of spending 3.5 per cent of gross domestic product on defence by 2035 but does not have a concrete plan to get there.
