Have bubbles on the cool. Will make any celebration special.
Invite customers, stakeholders, other departments, or other companies with shared interest. Make it special. Ensure invitation, music, dancing, entertainment. Maybe team up with an event bureau to make it extra special.
Have a Journal at the office. Use it as a diary to capture fun quotes, moments, milestones met, observations, learnings, etc. Add pictures, or other markers to remember the team’s shared history.
Do something special to mark releases. Dress up, put on a hat, put up a festoon of lights, paper, turn on a special light.