The former army major - a European Space Agency flight engineer - is blasting off from Baikonur in Kazakstan tomorrow with two American and Russian colleagues for a 171-day mission at the orbiting research outpost.
"We've been so busy focusing on this mission I forgot that Christmas is just a week away," Peake told reporters at the Cosmonaut Hotel in Baikonur today.
The 43-year-old added that he would be able to call his relatives from space to wish them a merry Christmas.
"I also heard that a Christmas pudding went up on orbital four so we will have treats as well," Peake said to laughter in the press room.
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The experienced air pilot will become only the eighth Briton to enter the cosmos after tomorrow's rocket launch, which is scheduled for around 1100 GMT.
He has vowed to take part in the London marathon from space on April 24, harnessed to a running machine on the ISS some 400 kilometres (250 miles) above Earth.
The trio will join up with the three astronauts already at the ISS - Scott Kelly of NASA and Russians Sergei Volkov and Mikhail Kornienko.
Three other astronauts - NASA's Kjell Lindgren, Japanese astronaut Kimiya Yui and Russian cosmonaut Oleg Kononenko - returned to Earth on Friday in a rare nighttime landing.
The ISS space laboratory has been orbiting the Earth at roughly 28,000 kilometres per hour since 1998.
Space travel has been one of the few areas of international cooperation between Russia and the West that has not been wrecked by the Ukraine crisis.