In an emergency you may need to have electricity. How do you get it?
The easiest way is to pull a small 12v electric motor from a car, the windshield wiper motor for example or the heater blower motor. Get a piece of crap bicycle. Shove a hunk of wood under the center of the bike and tie down the front wheel so the rear wheel is suspended. Pull the tire off the rear wheel. Cut up the inner tube to create a belt going from the bicycle rear wheel to the shaft of the small 12v motor. Start peddling and you start generating electricity. Attach the motor leads to something you want to run, like a light bulb and you have electricity.
Not very usable, you will notice the light is not consistent. This is because we need a battery and a voltage regulator to smooth out the system.
As soon as you connect the motor to the battery it will try to start the motor spinning. This is where a voltage regulator comes in handy. Most cars have them, although many are inside of the alternator.
Most car alternators are too demanding to spin using the kind of set-up I describe above. The smaller the alternator the easier it is, think Dodge Neon or some other really small car. Even then the electrical systems are so overloaded that the alternator might be too large to spin with a bicycle.
Most chainsaws have enough horse power to spin a car alternator. Again, you need to rig some kind of support structure to hold everything together, but, it will work. The same is true of any gasoline operated yard tool. Just disassemble the yard tool and rig it to the alternator. As crazy as this sounds tough rubber hose and hose clamps can be used to direct connect the shaft of a small gasoline engine to an alternator. Don't expect it to last very long with high loads though.
If you try and convert a lawnmower you need to replace the blade with a flywheel of some kind. A large diameter pully will work.
Most alternators are 100 amp or less so the most horsepower you need for an alternator is 3.5hp. For a 35amp alternator (you may, MAY) find this in a compact car you need about 1.2hp.
You could make a windmill from a bicycle wheel by wrapping aluminum foil around the spokes to create vanes. This won't produce a lot, but, using a rear wheel with a sprocket and rigging a chain to a small electric motor you can use it to power a small 12v radio. If you run the inner-tube belt around the outside of the wheel and rig the motor on some support you can use a front wheel.
Again, without some kind of rectifier, voltage regulator, etc, the power will be sporadic.
You can use automotive regulators although most are pretty wasteful of electricity.
This sounds a lot like McGyver kind of stuff and it is, although usually McGyver was way to technical to make the information useful.
The problem in a disaster is typically a lack of information and technical resources. By having any technical knowledge, such as just about all electric motors can generate the same amount of voltage they run on if something spins the motor, is valuable.
Figuring out how to transmit power from something spinning to a motor can be difficult, but, almost anything can work as a power transmission (fan) belt, even string.