Staff are the anniversary. They have built the organisation over the past five years. The party is as much theirs as the board's. How to really involve them:
Before the event: collect stories, memories and photos via an internal call or poll. Work these into a presentation, video, or exhibition during the party. During the event: let staff take the floor themselves, not just the director. A personal anecdote from a staff member who has been there since day one resonates more than a formal speech. After the event: share the highlights via internal channels. Let people take the celebration with them: literally, with a keepsake, and figuratively, with a sense of pride.