Hello.
It depends on what sensor you plan to use, how much mA the device needs, it is possible to "step-up" 3 volt to 5 volt.
Example:
https://www.sparkfun.com/products/10968One solution is to use a 5 volt power source to the sensor and "step-down" to 3 volt for the mcModule
Example:
https://www.pololu.com/product/2842Some of the devices that state 5 volt also runs just fine on 3 volt, so it's good to always read the schematic for the device.
Do you have any special device in mind?