Use common mechanical attachments with a standard bicycle using this one weird tip. Also, you won’t believe what happened next.
Background: A person can generate on the order of ~100W on a stationary bicycle for a half hour or so, for a total of 0.05kWh. This would be enough to power a space heater for about 3 minutes, or a low-draw 10 watt LED light for 5 hours.
There are already various electrical contraptions with batteries that allow a person to theoretically charge a laptop / phone using pedal power.
But there is currently no standard purely-mechanical interface to the bicycle!
In order to remedy this omission, there should be a standard interface that would allow any mechanical device to receive rotational energy from any bicycle, without requiring modifications to the bicycle. This could be useful in a post-apocalyptic scenario.
The basic plan would very similar to a bicycle-to-stationary bicycle conversion kit (examples: https://www.google.com/search?q=stationary+bicycle+conversion+kit ).
- It would consist of a roller that is driven by direct contact with the rear bike tire. (Although it would be more efficient to capture the rotational energy at the pedals, most methods of doing so would require at least some minor alterations to the bicycle  .)
- The roller would have a standard-sized drive gear on one end, which could be connected in order to power compatible equipment without the need for any electrical or battery-based intermediaries.
Such devices might include:
- A drill (with power transmitted through a cable, in the same way as an old-fashioned foot-pedaled dentist’s drill operates).
- A bike / car tire pump. Much easier than compressing a cylinder manually!
- A water pump, perhaps for drawing up water from a well.
- A sewing machine
- A blender
- An electric mixer
- A circular saw
Fig 1: Pedaling this now-stationary bicycle causes the back wheel (red) to drive the stationary-bicycle-style roller (blue), which then causes the attached gear to rotate (yellow). Additional to-be-powered devices can be attached to that gear at the point indicated by the orange arrow. (Note: although in this diagram the gear is connected to a long axle, the gear would presumably actually be directly attached to the roller.)
PROS: Lets you use various blending / cutting / etc. devices in a post-apocalyptic world without electricity or batteries. The standardization of this system would allow simpler development of additional devices to be powered in this fashion.
CONS: This proposed device would probably occupy a lot of space in a garage or closet, which would be wasted in the event that there is no post-apocalyptic world to cope with.
: For example, a gear could be interfaced directly with the front gear (avoiding the entire chain of transmission loss to the chain, rear wheel, and roller), or the chain could be attached to the front gear and used to directly power our drive gear / roller, avoiding the transmission loss with the roller and rear wheel.