Major birthdays - or minor ones for that matter. It's great to celebrate with family or friends, but why not make it a great celebration?
Transition celebrations - there doesn't come much bigger than a transition - whether it's a gender transition, celebrating the new you. Maybe a transition from married life to one as a single person. From working to a person of leisure in retirement. Maybe a new career? A celebration of coming out. Are you moving away, or going travelling?
Have you achieved something wonderful? Come on, why are you not celebrating this?
All should be celebrated.