Today's moments are tomorrow's memories.
Thoughts and memories.
Odin always has two ravens, Huginn (thoughts) and Muninn (memories). Legend says the ravens flew across the world each day to gather news of what was happening. They told Odin the information from the nine worlds over dinner.
Along with using his birds, Odin also had a view of everything that happened in the world from his throne in Asgard. Huginn and Muninn ensured that his knowledge did not rely entirely on his perception.