What are some brain activites that people can do to help prevent memory lost?

The brain's a muscle. Using the brain for active tasks of any kind helps preserve memory. Socialization with other people face to face is excellent both for verbal and non-verbal communication. Mild physical exercise is beneficial because it increases cerebral circulation. Doing puzzles of various sorts can be quite helpful. Playing games, such as checkers, chess or even video games can help. But lost memor is lost.
Keep working. There are exercises for memory. Google it.