(CBS News) AMESBURY, Mass. -- No one was closer to President John F. Kennedy than his longtime aide, Dave Powers.
After Powers died in 1998, his family discovered the treasure trove of history he'd acquired over the years. This weekend, it's going up for auction.
For the entirety of John F. Kennedy's political life, from his first campaign for Congress in 1946 through his presidency, Powers was at his side.
"They were literally together every day," says auction appraiser Dan Meader. "They traveled together on every campaign trip. Dave was with him every day."
In the White House, Powers was the president's personal assistant.
Among the items up for sale Sunday at John McInnis Auctioneers in Amesbury, Mass., are the presidential banner flown on official motorcades; the pen Kennedy used to order the interception of Soviet ships during the Cuban Missile Crisis; and the president's Air Force One bomber jacket, which has the highest estimate in the sale: $20,000 to $40,000.
It's hard to know how much the items will bring in, but Meader says, "that's the beauty of an auction."
Meader, who catalogued the thousands of items says one moved him especially: The official schedule of the president's trip to Dallas on Nov. 22, 1963.
Watch: Dallas begins year of observances for 50th anniversary of President John F. Kennedy's assassination, below.
Powers was riding in the Secret Service car behind the president that day, taking pictures before his film ran out.
Meader says Powers took his last photo at 12:17 p.m. Thirteen minutes later, Powers' schedule notes: "JFK shot." Minute by minute, he would detail the entire day.
Powers, who went on to run the Kennedy Presidential Library, stayed close to the president's widow. There are some 60 letters and notes from Jackie up for auction -- none more touching than the one inside a leather-bound book of presidential inaugural speeches.
"For Dave Powers," Mrs. Kennedy wrote. "The President was going to give you this for Christmas. Please accept it now from me. ... You and I will miss him most."
Powers' mementos tell the story of a political life that ended tragically -- and of a friendship that never died.
For more information on Sunday's auction, visit www.mcinnisauctions.com.