Re: a horn (if you already have a battery for lights)
Actually I have one of these on a trike plant bike that I used to use at work, pre-golf cart days. I powered it with a 12V SLA, 10AH battery and I was surprised how much use I got from a charge. In a warehouse environment where horns are used constantly by forklifts and other vehicles I wanted something unique so I put the Ahhhh-ooo-Gaaa horn on my trike. I would charge it once a week and used the horn probably ten times more than a biker would need it. Of course the battery didn't share the load with lights but unless you do a lot of after dark riding Jason's horn would probably work just fine. You need to consider weight however. My horn weighs about 2 pounds.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"