Copy something, copy something else, and the first item is gone. A clipboard manager keeps a history so you can paste anything from the last hour or the last week.
Windows and Mac already have a basic one
On Windows, press the Windows key and V to turn on clipboard history. On a Mac you'll need a separate app, and several good ones are free.
Keep passwords out of it
A clipboard history also remembers passwords you copy. Good managers skip anything copied from a password manager automatically; check that setting before you rely on one.