How do I connect light bulbs to an alternator on a bike?
You have several problems to solve on the way to a viable solution:


The alternator does not begin to regulate it's output until the speed is quite high (1500 rpm or above). So you'll need to configure your gearing so you spin the alternator quite fast.
Looking at your datasheet you can see your likely area of operation in the 1000-1500 rpm area.




Even at just 1500 rpm and 50% efficiency (the worst it could be) you have the potential to generate about 360 W of power and be within the bounds of human effort. Your pedal cadence is likely to be about 70-80 rpm at best so you will need a total gear ratios 18-22:1 to drive the alternator. 


Many alternators won't start if they have no voltage on the load side (they normally have a battery, even if it's a bit flat). If there is no battery as in your scenario you need to give it some help. I'd suggest you connect something like a 1000-4000 uF capacitor across the output, this will help stabilize the rotor current and help bootstrap the alternator. 
When it does start to regulate it wants to set the voltage to about 13.8-15 V, this is the voltage normally required to charge/top-up a lead acid battery (13.8 V fully charged). You will be able to run 12 Volt auto globes or many of the 12 V LED lights you find at this voltage without having to worry about series resistors.
Human power output varies. If you use a sports fit person you might be able to get 500 W easily (https://en.wikipedia.org/wiki/Human-powered_transport).
You will lose some power to the voltage/current required for the rotor but the alternator efficiency should be about 60% or higher at the lower rpms you'll be able to achieve. You can also get a marginal increase in the overall efficiency by removing the fan on the front of the alternator since you won't generate much heat in the alternator.


 


Don't plan on spinning the alternator much beyond about 2000 rpm as the efficiency (losses increase) drops with higher rpms.
You could also replace the internal 3 phase bridge with more modern (and low forward voltage) Schottky diodes and boost efficiency by another 10-15%.


Note: You could also consider that there are alternative motor types that can be used very effectively as a generator. For example if you use an RC Outrunner Brushless motor, these work well as generators. The difference here is that there is no field to power (it has magnets) and the output voltage varies almost linearly with rotational speed. You could feed one of these into a 3 phase rectifier/capacitor and use a SM DC/DC convertor to regulate back to 12 V.