Half a decade in, and the cake usually gets a theme of its own. A single 4-inch plastic 5 on a pick sits on top of whatever that theme is without fighting it, which is more than a full character set does.

Also the second digit for a 15th, 25th, 35th and so on when paired with another pick. Sold by the package (1 cake topper) or by the case (12 cake toppers).