A keepsake is an object that has sentimental value, like a locket that belonged to your grandmother.
In one of the Batman movies, Bruce Wayne keeps the pearls his mother wore the day she was murdered. Those pearls are a keepsake: something that has great meaning because of its association with a person. Many parents keep pictures their kids drew as keepsakes. If you loved a job, you might have a keepsake from it. Souvenirs from fun vacations are keepsakes. A keepsake is something we keep for the sake of the people and events we want to always remember.