Some fun ways to celebrate Boss's Day are going out for lunch, bringing a cake into the office, giving a gift and giving a card. Boss's Day is not a well-known holiday, so low-key celebrations are appropriate in most offices.
For employees who like the idea of a celebration, baking or buying a cake can make the day feel special. Bringing lunch into the office, going out for lunch or going out for dinner after work can also be nice ways to spend time with a boss. Hosting a potluck party where every employee brings a dish, snack or treat can help people get to know each other better.
For employees who prefer to give something to their boss, having everyone contribute a small amount to purchase a nice gift can be a good idea. An item that has personal meaning or relates to the boss's hobbies or interests will be appreciated. If a gift seems too personal or expensive, then a nice card signed by all the employees might be a better choice. A written message of appreciation might be what a boss enjoys the most. For a less serious choice, creating an award or trophy celebrating something likable about the boss would be fun.