First, the rationale: I don't want lights on my bike because they're theft magnets, are more fragile, and more cumbersome. I want a single battery pack that powers a tail light and one or two headlights, and I want to turn it all on or off with one switch. The backpack is the best way to go for me, since I also like to carry my lock in the backpack anyway and always have it with me.
I used two Luxeon Rebel Stars (145 lumens @ 700mA) for the headlights, and two Luxeon III red-orange side emitters for the tail light. I made a little 555 timer circuit (google it) and encased it in epoxy, and rigged up a switch so that the tail light is always blinking, but the headlights can blink or be solid. Due to my electronics half-assery, the headlights actually blink very slightly when "solid." You can't really tell when riding, though.
I went the resistor route instead of using a buckpuck, which I somewhat regret. A buckpuck is especially cool because you can later upgrade to a Li-ion battery pack (much more convenient to charge, and lighter) and it'll still work the same even though the input voltage is different. And it wastes less juice and thus produces less waste heat.
The switches I used are waterproof E-Switch 100AWSP1's, mouser part # 612-100A-A1422 / manuf. part # 100AWSP1T1B4M2RE.
A good place to go for 555 circuit:
Step 1: Wiring
I also used fairly heavy gauge speaker wire which made it a little more clunky than necessary.
Step 2: Tail Light
Even though the color of the LEDs is called red-orange, it's pretty much red. It's the same color as a car tail light. Red-orange is more visible than "real" red. The two Luxeon IIIs make for quite a bright tail light, although the headlights get all the compliments. On to those...
Step 3: Headlights
The Rebel Stars I used put out 145 lumens @ 700mA. You can get ones up to 180 lumens @ 700 mA. Compare this to a Luxeon III which is 80 lumens @ 1000mA, or Luxeon K2s putting out 75 Lumens @ 700mA or 130 Lumens @ 1500mA. And you can actually run the Rebels at 1000mA, which could get you up to maybe 200 lumens. As I said in the intro, I don't remember exactly what kind of juice I wired them up for, but I believe it was in the neighborhood of 500mA each.
The headlight on the right was the first, and crappier, iteration. I tried using epoxy and that didn't work so well. The left is how I would do it if I were to make another set of these. They're pretty much completely exposed, but they seem to be ok with that. The actual Rebel LED part has this little clear rubber bubble thing, which is pretty fragile and soon was ripped off of each one. But it didn't noticeably change the optics. JB Weld holds them on and seals off the contacts. For each light, I pressed the spiky sides of two heatsinks into each other, which then gave me these slots that I could run zip ties through to attach them to the backpack straps with.
And that's pretty much it!