My bikes have the usual stuff - lights, bell, computer.
The Maximus I ride at work has an air freshener...
It's little thing with a bottle of lavendish (smells like lavender, sort of) liquid, and a wick, and on the top a little fan that presumably is designed to turn in a breeze and waft the scent across the room. I found it in a recycling box, and stuck it to the bars with a rubber band - and now the fan spins round when the trike goes along.