9 watts of tail-lights! Make sure you don't blind the guy behind you when you hit your brakes at night!
As for small DC/DC converters, I have one very similar to this one currently posted on Ebay.
DC-to-DC Converter 100W 48V to 3.3V, 12V, 12V Very Nice - eBay (item 220301819466 end time Nov-02-08 17:13:02 PST)
I was able to get mine for $10, and the guy had a couple of them, so I bought two. The original is on my electric motorcycle, and I am planning to use the other one on my Citicar.
This one posted has two 50 watt outputs on it. Maybe run one to your headlight, and one to everything else, or both to your battery.
That 3.3 V output might also be useful for directly running LEDs?