The 1870s flagstaff is being repaired in time for the 700th anniversary of the Battle of Bannockburn next year. The capsule dates back to 1937, when King George VI was crowned.
The flagpole was replaced that year after storm damage.
The capsule contains a newspaper from that year, a thimble, a metal token, a 1911 Falkirk coronation medal, a 1924 farthing, a half-crown from 1928 and bits of a brown glass vessel.
National Trust for Scotland curator Alastair Smith said: "The 1937 Bannockburn capsule commemorates the coronation year, though many of the objects may have been added on the spur of the moment. The bottle may have been smashed in the way ships have been launched."
Rory MacLeod of Fife said his grandfather was involved. He said: "He was managing director of the Grangemouth Dockyard Co that worked on the repairs to the top section and decided to include a capsule. He wanted to leave objects he felt were representative of that time, and the pride the firm had in repairing part of a historic monument."
The flagpole has been replaced, and a weather vane styled on Robert the Bruce's battleaxe has been created.