Writing. Painting. Composing music.
Those are the ways that humans have created to preserve parts of themselves. I would advice against preserving memories, though. Simply enjoy the moments you go through, senses can't accurately represent what we feel, and that might leave you frustrated (hobbies are always nice, though. We all need to express ourselves, and that is good for you and everyone else).
Still, if you can't enjoy what you identify as happy, you either might want to consider talking to a therapist, or the constructs of "joy" you have inside your head are not yours.
Therapy always helps, nonetheless.