More than 200 items from the Titanic, including a locker key and letters, are to be auctioned later.
The key to a life-jacket cupboard was used by a steward to save lives as the liner sank in 1912. It could fetch up to £50,000, according to estimates.
A letter to be sold reveals a senior officer had a "queer feeling" about his posting to the ship.
Saturday's auction in Devizes is one of the biggest involving Titanic memorabilia for many years.
RMS Titanic had been four days into a week-long transatlantic crossing from Southampton to New York when the supposedly "unsinkable" ship struck an iceberg on 14 April 1912.
The ship sank less than three hours later at about 02:20 on 15 April. More than 1,500 passengers and crew were killed.
The letter is part of a collection written over a 20-year period by Chief Officer Henry Wilde, who was second in command to the ship's skipper, Captain Edward Smith.
Wilde had been expecting to take command of another ship, the Cymric, and only signed on to the Titanic on 9 April 1912, the day before it sailed.
On 31 March 1912, he said he was "awfully disappointed to find the arrangements for my taking command of the Cymric have altered. I am now going to join the Titanic until some other ship turns up for me".
In another letter to his sister, written onboard Titanic and posted at Queenstown (now Cobh) in Ireland, he indicated he had misgivings about the new ship.
"I still don't like this ship... I have a queer feeling about it," he wrote.
After the collision, Wilde took charge of the even-numbered lifeboats, and oversaw their loading and lowering into the water. He was among those who died in the tragedy.
Auctioneer Andrew Aldridge, of Henry Aldridge & Son, said: "It is without doubt one of the finest Titanic-related letters, written by one of the liner's most senior officers on Olympic stationery.
"This lot reveals previously unknown details and shows Wilde's obvious disappointment in being transferred to Titanic.
"What is certain is that he worked diligently to load the boats once the seriousness of the situation was clear to him."
Also included in the sale is a postcard from the ship's senior wireless operator, 25-year-old Jack Phillips, from Farncombe in Surrey, who carried on sending distress messages to other ships as the Titanic sank.
Phillips, who drowned, was described as "the man who saved us all" by survivor and fellow wireless operator Harold Bridge.
The card, signed "Love all, Jack", describes the weather as the ship left Cowes, Isle of Wight. It is expected to fetch about £20,000.
Rare photos of Smith could sell for £1,000 each, the auction house has estimated.